Variability in recruitment results in variability in catch from year-to-year, which is a problem for fishermen, for the processing industry and for fisheries managers. It is commonplace to read how large the interannual variability in recruitment can be and how difficult it is to determine the causes. However for an ecologist, the astonishing feature of recruitment variability is how small it is, given that fish produce thousands or millions of eggs each and that survival is extremely unlikely and uncertain. Among the pelagic and demersal stocks assessed in the NE Atlantic the smallest year-class is generally within a factor of 10 of the biggest. It is not infrequent for interannual recruitment variability to be less than the variability of the spawning biomass of the stock (Brander, 2003). How is the variability damped out? What are the compensatory mechanisms? Density dependence is necessary for populations to remain within feasible bounds (Reddingius, 1971) but as Ed told us “A little density dependence, especially in the relatively long juvenile stage, can regulate recruitment”. Density dependence should not be invoked without good evidence in relation to processes like adult growth, however appealing it is to biologists or convenient for modellers trying to keep their models stable. Fisheries assessment and management, at least in the North Atlantic, has focussed on year-to-year tracking of stock biomass in order to set annual catch limits. Questions about the role of recruitment were therefore also principally directed at annual prediction and the understanding of processes needed in order to do this. The biological book-keeping was done using sequential population analysis which gives estimates of both annual recruitment and spawning stock biomass (SSB). The latter is assumed to represent spawning output of the stock, but as many of the papers in this symposium show, fecundity, maturity, spawning frequency and egg quality, are not constant. The relevance of the symposium is therefore obvious, since strategies for sustainable management, using precautionary reference levels of SSB and fishing mortality, are based on the relationship between SSB and recruitment. We need to move on to a longer term view which includes a wider range of information about the biological state of fish, their environment and their interaction with the rest of the marine ecosystem. Ed once more: “’Solving the recruitment problem’ is no longer the holy grail of fishery science. Appreciating recruitment variability, explaining probable causes, considering implications for management, and understanding it in the context of broader variability in marine ecosystems are worthy goals.”
{"title":"Summing up - Symposium on reproductive and recruitment processes of exploited marine fish stocks","authors":"K. Brander","doi":"10.2960/J.V41.M640","DOIUrl":"https://doi.org/10.2960/J.V41.M640","url":null,"abstract":"Variability in recruitment results in variability in catch from year-to-year, which is a problem for fishermen, for the processing industry and for fisheries managers. It is commonplace to read how large the interannual variability in recruitment can be and how difficult it is to determine the causes. However for an ecologist, the astonishing feature of recruitment variability is how small it is, given that fish produce thousands or millions of eggs each and that survival is extremely unlikely and uncertain. Among the pelagic and demersal stocks assessed in the NE Atlantic the smallest year-class is generally within a factor of 10 of the biggest. It is not infrequent for interannual recruitment variability to be less than the variability of the spawning biomass of the stock (Brander, 2003). How is the variability damped out? What are the compensatory mechanisms? Density dependence is necessary for populations to remain within feasible bounds (Reddingius, 1971) but as Ed told us “A little density dependence, especially in the relatively long juvenile stage, can regulate recruitment”. Density dependence should not be invoked without good evidence in relation to processes like adult growth, however appealing it is to biologists or convenient for modellers trying to keep their models stable. Fisheries assessment and management, at least in the North Atlantic, has focussed on year-to-year tracking of stock biomass in order to set annual catch limits. Questions about the role of recruitment were therefore also principally directed at annual prediction and the understanding of processes needed in order to do this. The biological book-keeping was done using sequential population analysis which gives estimates of both annual recruitment and spawning stock biomass (SSB). The latter is assumed to represent spawning output of the stock, but as many of the papers in this symposium show, fecundity, maturity, spawning frequency and egg quality, are not constant. The relevance of the symposium is therefore obvious, since strategies for sustainable management, using precautionary reference levels of SSB and fishing mortality, are based on the relationship between SSB and recruitment. We need to move on to a longer term view which includes a wider range of information about the biological state of fish, their environment and their interaction with the rest of the marine ecosystem. Ed once more: “’Solving the recruitment problem’ is no longer the holy grail of fishery science. Appreciating recruitment variability, explaining probable causes, considering implications for management, and understanding it in the context of broader variability in marine ecosystems are worthy goals.”","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tanner crab (Chionoecetes bairdi) in the eastern Bering Sea are primarily distributed in Bristol Bay and around the Pribilof Islands. Summer trawl survey data in these two areas were used to estimate mean sizes at maturity for female Tanner crab from 1975 to 2006 and sizes at 50% morphometric maturity for male Tanner crab from 1990 to 2006. Estimated mean sizes at maturity for females showed a statistically significant downward trend in both areas. Sizes at 50% morphometric maturity for males have declined significantly since 1990, in Bristol Bay only. In Bristol Bay, the distribution centers of female Tanner crab have shifted southwest over time and the decrease in female mean size at maturity was significantly related to changes in longitude and bottom depths. Because of terminal molt at maturity, the decrease in size at maturity has important implications for fisheries management: under the current size limit, a smaller proportion of males grow to legal size and therefore a higher proportion of large-growing males are removed by the fishery before they have a chance to participate in reproduction. With the recent maturity at a small size, reduction of the current harvest rates and size limit while maintaining current fishing gear requirements will result in higher yield and higher male spawning biomass per recruit than those under the current harvest strategy.
{"title":"Temporal Changes in Size at Maturity and Their Implications for Fisheries Management for Eastern Bering Sea Tanner Crab","authors":"J. Zheng","doi":"10.2960/J.V41.M623","DOIUrl":"https://doi.org/10.2960/J.V41.M623","url":null,"abstract":"Tanner crab (Chionoecetes bairdi) in the eastern Bering Sea are primarily distributed in Bristol Bay and around the Pribilof Islands. Summer trawl survey data in these two areas were used to estimate mean sizes at maturity for female Tanner crab from 1975 to 2006 and sizes at 50% morphometric maturity for male Tanner crab from 1990 to 2006. Estimated mean sizes at maturity for females showed a statistically significant downward trend in both areas. Sizes at 50% morphometric maturity for males have declined significantly since 1990, in Bristol Bay only. In Bristol Bay, the distribution centers of female Tanner crab have shifted southwest over time and the decrease in female mean size at maturity was significantly related to changes in longitude and bottom depths. Because of terminal molt at maturity, the decrease in size at maturity has important implications for fisheries management: under the current size limit, a smaller proportion of males grow to legal size and therefore a higher proportion of large-growing males are removed by the fishery before they have a chance to participate in reproduction. With the recent maturity at a small size, reduction of the current harvest rates and size limit while maintaining current fishing gear requirements will result in higher yield and higher male spawning biomass per recruit than those under the current harvest strategy.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We hypothesized that faster growth during the larval and juvenile stages results in higher survival in Pacific sardine (Sardinops sagax) in the California Current region. Growth rate estimated from the width of otolith daily increments was compared among larval, juvenile and pre-recruit S. sagax spawned in 2004 and 2006. Larvae, juveniles and pre-recruits were collected in spring, autumn and the spring of the subsequent year, respectively. Hatch-date distribution of the pre-recruits ranged from April to August with peaks in late spring and summer, corresponding to the seasons of spawning and larval production in the Southern California Bight. The pre-recruits, from eggs hatched in the late spring, were assumed to originate from the larvae and juveniles from eggs hatched in April to June. Fish collected as pre-recruits grew faster than those collected as juveniles during the 3–5 months after hatching. Growth-selective survival for the late spring-hatched cohorts took place during July–November for the early juveniles. These results are consistent with the hypothesis that early juveniles with faster growth rate during summer and autumn had a higher probability of survival to the adult stock in the California Current region.
{"title":"Growth and Survival of Pacific Sardine (Sardinops sagax) in the California Current Region","authors":"M. Takahashi, D. Checkley","doi":"10.2960/J.V41.M626","DOIUrl":"https://doi.org/10.2960/J.V41.M626","url":null,"abstract":"We hypothesized that faster growth during the larval and juvenile stages results in higher survival in Pacific sardine (Sardinops sagax) in the California Current region. Growth rate estimated from the width of otolith daily increments was compared among larval, juvenile and pre-recruit S. sagax spawned in 2004 and 2006. Larvae, juveniles and pre-recruits were collected in spring, autumn and the spring of the subsequent year, respectively. Hatch-date distribution of the pre-recruits ranged from April to August with peaks in late spring and summer, corresponding to the seasons of spawning and larval production in the Southern California Bight. The pre-recruits, from eggs hatched in the late spring, were assumed to originate from the larvae and juveniles from eggs hatched in April to June. Fish collected as pre-recruits grew faster than those collected as juveniles during the 3–5 months after hatching. Growth-selective survival for the late spring-hatched cohorts took place during July–November for the early juveniles. These results are consistent with the hypothesis that early juveniles with faster growth rate during summer and autumn had a higher probability of survival to the adult stock in the California Current region.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Georges Bank Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stocks have undergone significant changes over the last 40 years with the reduction of older spawners and increased incidence of young mature fish. Captive studies, from other investigations, have noted that firstand second-time spawners exhibit lower egg hatching success, and especially for haddock compared to cod. Spawning stock biomass (SSB), derived from virtual population analysis (VPA), has been considered as an overestimate of a stock’s spawning potential since it does not fully account for differences in age or size of spawners. The Northeast Fisheries Science Center’s (NEFSC) ichthyoplankton Surveys (1979–1999) have provided an independent estimate of seasonal egg production to compare with a VPA-fecundity based estimate. Since the early stage eggs of the two species are indistinguishable, their numbers were estimated by apportioning the total egg abundance (cod plus haddock) at a station by the late stage abundance ratio, assuming equal mortality for the two species. For cod, the Surveys overestimated the VPA-derived egg production in many years by as much as an order of magnitude. However, for haddock, the VPA-derived egg production estimates were mostly higher than those from the Surveys. Comparing the ratio of the two egg production estimates versus the total combined VPA egg production of cod and haddock, the cod ratios were high when haddock was abundant, especially during the years 1995–1999, and closer to one when cod comprised the greater part of the total. The corresponding analysis for haddock was the reverse to that of cod further supporting the hypothesis that the higher egg mortality of the reduced age population of haddock biased the seasonal egg production estimates of both haddock and cod. These ratios appear to explain 60–70% of the variability in the ratio of Survey to VPA seasonal egg production, while other factors might be related to fecundity and age-class composition of the SSB, or changes in egg mortality rates over the time series. Our Survey estimates also suggest that haddock egg mortality is greater than cod. Thus, the seasonal egg production estimates from egg Surveys based on constant egg mortality are probably inaccurate, especially since the mid-1990s. Cod egg production may have been overestimated and haddock’s underestimated.
{"title":"Differential Egg Mortality of Georges Bank Cod and Haddock Inferred from Two Independent Estimates of Seasonal Egg Production","authors":"R. Lough, L. O’Brien, L. Buckley","doi":"10.2960/J.V41.M625","DOIUrl":"https://doi.org/10.2960/J.V41.M625","url":null,"abstract":"Georges Bank Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stocks have undergone significant changes over the last 40 years with the reduction of older spawners and increased incidence of young mature fish. Captive studies, from other investigations, have noted that firstand second-time spawners exhibit lower egg hatching success, and especially for haddock compared to cod. Spawning stock biomass (SSB), derived from virtual population analysis (VPA), has been considered as an overestimate of a stock’s spawning potential since it does not fully account for differences in age or size of spawners. The Northeast Fisheries Science Center’s (NEFSC) ichthyoplankton Surveys (1979–1999) have provided an independent estimate of seasonal egg production to compare with a VPA-fecundity based estimate. Since the early stage eggs of the two species are indistinguishable, their numbers were estimated by apportioning the total egg abundance (cod plus haddock) at a station by the late stage abundance ratio, assuming equal mortality for the two species. For cod, the Surveys overestimated the VPA-derived egg production in many years by as much as an order of magnitude. However, for haddock, the VPA-derived egg production estimates were mostly higher than those from the Surveys. Comparing the ratio of the two egg production estimates versus the total combined VPA egg production of cod and haddock, the cod ratios were high when haddock was abundant, especially during the years 1995–1999, and closer to one when cod comprised the greater part of the total. The corresponding analysis for haddock was the reverse to that of cod further supporting the hypothesis that the higher egg mortality of the reduced age population of haddock biased the seasonal egg production estimates of both haddock and cod. These ratios appear to explain 60–70% of the variability in the ratio of Survey to VPA seasonal egg production, while other factors might be related to fecundity and age-class composition of the SSB, or changes in egg mortality rates over the time series. Our Survey estimates also suggest that haddock egg mortality is greater than cod. Thus, the seasonal egg production estimates from egg Surveys based on constant egg mortality are probably inaccurate, especially since the mid-1990s. Cod egg production may have been overestimated and haddock’s underestimated.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
After the absence of 1989–1994 year classes of Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides) in regular surveys, an annual survey programme was initiated in 1996 to map juveniles in previously unsurveyed waters north and east of Svalbard. After rather stable juvenile indices in the first years, the recruitment indices have increased tenfold from 2001 to 2006. The increase in juvenile Northeast Arctic (NEA) Greenland halibut corresponded with an increase in spawning stock biomass. The swept area abundance estimates of spawning females (i.e., females >60 cm), has nearly tripled since 1996 having achieved 29 000 t in recent years. This improvement occurred after years of strong regulations, introduced in 1992, by enforcing a moratorium on the targeted offshore fishery and strict bycatch regulations for the species. Regulations were introduced after a dramatic change in stock status for the NEA Greenland halibut during the 1980s. Females >75 cm contributed more to the stock’s total egg production (TEP) in more recent years. The contribution from these larger females increased from 10% of the TEP estimate in 1996 to 21% in 2006. The results from the present study indicate that rebuilding Greenland halibut stocks takes time, and that at least 12–15 years with restrictions are needed to recover from the low levels observed in the Barents Sea in the beginning of the 1990s.
{"title":"Rebuilding the Stock of Northeast Arctic Greenland Halibut (Reinhardtius hippoglossoides)","authors":"Å. Høines, A. C. Gundersen","doi":"10.2960/J.V41.M618","DOIUrl":"https://doi.org/10.2960/J.V41.M618","url":null,"abstract":"After the absence of 1989–1994 year classes of Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides) in regular surveys, an annual survey programme was initiated in 1996 to map juveniles in previously unsurveyed waters north and east of Svalbard. After rather stable juvenile indices in the first years, the recruitment indices have increased tenfold from 2001 to 2006. The increase in juvenile Northeast Arctic (NEA) Greenland halibut corresponded with an increase in spawning stock biomass. The swept area abundance estimates of spawning females (i.e., females >60 cm), has nearly tripled since 1996 having achieved 29 000 t in recent years. This improvement occurred after years of strong regulations, introduced in 1992, by enforcing a moratorium on the targeted offshore fishery and strict bycatch regulations for the species. Regulations were introduced after a dramatic change in stock status for the NEA Greenland halibut during the 1980s. Females >75 cm contributed more to the stock’s total egg production (TEP) in more recent years. The contribution from these larger females increased from 10% of the TEP estimate in 1996 to 21% in 2006. The results from the present study indicate that rebuilding Greenland halibut stocks takes time, and that at least 12–15 years with restrictions are needed to recover from the low levels observed in the Barents Sea in the beginning of the 1990s.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reproductive success, best defined as lifetime total offspring to reach maturity, is the product of the number of eggs produced (i.e., fecundity) per season, adult reproductive life span and offspring survival to maturity. Life history traits at the population level can be seen as a representation of the fate of individuals through their life cycle. For practical purposes, reproductive success is often separated in two components: reproductive potential and offspring survival to maturity. In studies of exploited marine fish populations, spawning stock biomass (SSB) is commonly used as a proxy of reproductive potential instead of direct measures of the egg production of the stock. This technique assumes, however, that egg production per unit of biomass is time-invariant. This assumption is unsupported by a review of the literature. Seasonal fecundity varies in relation to parental quality (e.g., size, condition), resource availability (e.g., food abundance and quality), environmental (e.g., temperature) and evolutionary factors (e.g. stock biomass, fishing pressure). Recent studies and use of generalized linear models to hindcast fecundity variations demonstrate that stock reproductive potential estimated by the total egg production can lead to different perceptions of the state and productivity of the stock. The recent development of cost-effective methods to count egg numbers of fish now makes it practical to routinely determine potential fecundity. Adding measures of fecundity to other demographic parameters that are already commonly measured for exploited marine fish stocks allows a more precise measurement of the reproductive potential. One possible outcome of measuring reproductive potential as demonstrated using northern Gulf of St. Lawrence cod as a case study is the calculation of the intrinsic rate of population increase (r), an essential parameter in population dynamics and evolutionary ecology, which can be used in determining sustainable harvesting, resilience, and potential rates of recovery of populations.
{"title":"Why Should We Closely Monitor Fecundity in Marine Fish Populations","authors":"Y. Lambert","doi":"10.2960/J.V41.M628","DOIUrl":"https://doi.org/10.2960/J.V41.M628","url":null,"abstract":"Reproductive success, best defined as lifetime total offspring to reach maturity, is the product of the number of eggs produced (i.e., fecundity) per season, adult reproductive life span and offspring survival to maturity. Life history traits at the population level can be seen as a representation of the fate of individuals through their life cycle. For practical purposes, reproductive success is often separated in two components: reproductive potential and offspring survival to maturity. In studies of exploited marine fish populations, spawning stock biomass (SSB) is commonly used as a proxy of reproductive potential instead of direct measures of the egg production of the stock. This technique assumes, however, that egg production per unit of biomass is time-invariant. This assumption is unsupported by a review of the literature. Seasonal fecundity varies in relation to parental quality (e.g., size, condition), resource availability (e.g., food abundance and quality), environmental (e.g., temperature) and evolutionary factors (e.g. stock biomass, fishing pressure). Recent studies and use of generalized linear models to hindcast fecundity variations demonstrate that stock reproductive potential estimated by the total egg production can lead to different perceptions of the state and productivity of the stock. The recent development of cost-effective methods to count egg numbers of fish now makes it practical to routinely determine potential fecundity. Adding measures of fecundity to other demographic parameters that are already commonly measured for exploited marine fish stocks allows a more precise measurement of the reproductive potential. One possible outcome of measuring reproductive potential as demonstrated using northern Gulf of St. Lawrence cod as a case study is the calculation of the intrinsic rate of population increase (r), an essential parameter in population dynamics and evolutionary ecology, which can be used in determining sustainable harvesting, resilience, and potential rates of recovery of populations.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Japanese sea bass larvae migrate from Ariake Bay, southwestern Japan, into the Chikugo Estuary and inhabit there throughout the juvenile period. Abundance of Japanese sea bass larvae and juveniles in the estuary shows a 40-fold fluctuation, higher than that in adult stock (2-fold). It is likely that a density-independent mechanism seems to influence the survival of larval (pre-immigration) period and that a density-dependent mechanism regulates the survival during the juvenile (postimmigration) period. We tested the hypotheses that physical conditions such as freshwater discharge and temperature influence pre-immigration survival through affecting larval growth rate and that a density-dependent mechanism regulates post-immigration survival of the Japanese sea bass. Mean larval growth rate (G15, mm d -1) during the pre-immigration period (<15 mm), weight-specific growth coefficient (Gw, d -1), mortality coefficient (M, d-1), and relative recruitment potential (Gw/M) during the postimmigration period (15–20 mm) were estimated from 1990–2000. Freshwater discharge through the Chikugo River had a significant effect on the temperature of the upper Ariake Bay. The G15 varied between 0.04 and 0.10 mm d -1 and was significantly correlated with the temperature experienced by the larvae. The G15 had a significant effect on the larval and juvenile sea bass abundance, with higher abundance in years with high G15. Freshwater discharge seems to be a primary factor for the density-independent control of larval Japanese sea bass survival, influencing water temperature in the upper Ariake Bay and the larval growth. The Gw/M was significantly affected by the Japanese sea bass abundance at 15 mm: lower Gw/M in years of high abundance. Density-dependent regulation seems to operate on the post-immigration Japanese sea bass in the Chikugo Estuary.
日本黑鲈幼鱼从日本西南部的有明湾迁徙到千古河口，并在那里度过整个幼年期。河口黑鲈幼鱼和幼鱼的丰度波动幅度为40倍，高于成鱼的2倍。很可能是一种不依赖于密度的机制影响了幼虫(迁徙前)的生存，而一种依赖于密度的机制调节了幼鱼(迁徙后)的生存。我们测试了物理条件(如淡水排放和温度)通过影响幼虫生长速率影响迁移前生存的假设，以及密度依赖机制调节迁移后日本海鲈鱼的生存。在1990-2000年期间估计了迁入前(<15 mm)的平均幼虫生长率(G15, mm d-1)、体重特异性生长系数(Gw, d-1)、死亡率系数(M, d-1)和迁入后(15 - 20 mm)的相对招募潜力(Gw/M)。通过赤果河的淡水排放对有明湾上游的温度有显著影响。G15变化范围为0.04 ~ 0.10 mm d -1，与幼虫所经历的温度呈极显著相关。G15对鲈鱼幼鱼和幼鱼的丰度有显著影响，在G15高的年份丰度较高。淡水放水量对有明湾上游水温和鲈鱼幼鱼的生长有重要影响，是控制鲈鱼幼鱼存活率的主要因素。Gw/M受15 mm处黑鲈丰度的影响显著，高丰度年份的Gw/M较低。密度依赖性调节似乎在千古河口的移民后日本海鲈鱼身上起作用。
{"title":"Recruitment Processes of Japanese Sea Bass in the Chikugo Estuary, Japan: Shift from Density-Independence to Density-Dependence During the Early Life Stages","authors":"J. Shoji, M. Tanaka","doi":"10.2960/J.V41.M612","DOIUrl":"https://doi.org/10.2960/J.V41.M612","url":null,"abstract":"Japanese sea bass larvae migrate from Ariake Bay, southwestern Japan, into the Chikugo Estuary and inhabit there throughout the juvenile period. Abundance of Japanese sea bass larvae and juveniles in the estuary shows a 40-fold fluctuation, higher than that in adult stock (2-fold). It is likely that a density-independent mechanism seems to influence the survival of larval (pre-immigration) period and that a density-dependent mechanism regulates the survival during the juvenile (postimmigration) period. We tested the hypotheses that physical conditions such as freshwater discharge and temperature influence pre-immigration survival through affecting larval growth rate and that a density-dependent mechanism regulates post-immigration survival of the Japanese sea bass. Mean larval growth rate (G15, mm d -1) during the pre-immigration period (<15 mm), weight-specific growth coefficient (Gw, d -1), mortality coefficient (M, d-1), and relative recruitment potential (Gw/M) during the postimmigration period (15–20 mm) were estimated from 1990–2000. Freshwater discharge through the Chikugo River had a significant effect on the temperature of the upper Ariake Bay. The G15 varied between 0.04 and 0.10 mm d -1 and was significantly correlated with the temperature experienced by the larvae. The G15 had a significant effect on the larval and juvenile sea bass abundance, with higher abundance in years with high G15. Freshwater discharge seems to be a primary factor for the density-independent control of larval Japanese sea bass survival, influencing water temperature in the upper Ariake Bay and the larval growth. The Gw/M was significantly affected by the Japanese sea bass abundance at 15 mm: lower Gw/M in years of high abundance. Density-dependent regulation seems to operate on the post-immigration Japanese sea bass in the Chikugo Estuary.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Early in the 20 th century, Johan Hjort developed compelling arguments and hypotheses to explain recruitment variability that became dominant for more than 75 years. A cautious emergence from Hjort’s shadow began late in the 20 th century. Hjort’s “Critical Period” hypothesis, i.e., failure of first-feeding larvae to find food, and a second hypothesis, “Aberrant Drift” of eggs and larvae, were proposed to explain causes of recruitment variability. Tests of the Critical Period hypothesis became an obsession, although support for it was inconsistent and equivocal. Single-minded research on the Critical Period hypothesis gave way to realization that recruitment variability was the outcome of complex trophodynamic and physical processes acting over many temporal and spatial scales and throughout pre-recruit life. A complex mix of main effects and interacting factors can easily generate order-ofmagnitude variability in recruitment via small effects on mortality and growth rates during the abundant egg and larval stages, or via cumulative effects during the pre-recruit juvenile stage. New considerations of compensatory mechanisms that can dampen variability and stabilize recruitment emerged. A little density dependence, especially in the relatively long juvenile stage, can regulate recruitment. Multidisciplinary programs instituted in the 1990s and successful development of statistical models and coupled bio-physical models, offered new insights into mechanisms generating recruitment variability. Despite progress, forecasting recruitment remains a formidable challenge. “Solving the recruitment problem” is no longer the Holy Grail of fishery science. Appreciating recruitment variability, explain ing its probable causes, considering implications for management, and understanding it in the context of broader variability in marine ecosystems, are all worthy goals.
{"title":"Emerging from Hjort's Shadow","authors":"E. Houde","doi":"10.2960/J.V41.M634","DOIUrl":"https://doi.org/10.2960/J.V41.M634","url":null,"abstract":"Early in the 20 th century, Johan Hjort developed compelling arguments and hypotheses to explain recruitment variability that became dominant for more than 75 years. A cautious emergence from Hjort’s shadow began late in the 20 th century. Hjort’s “Critical Period” hypothesis, i.e., failure of first-feeding larvae to find food, and a second hypothesis, “Aberrant Drift” of eggs and larvae, were proposed to explain causes of recruitment variability. Tests of the Critical Period hypothesis became an obsession, although support for it was inconsistent and equivocal. Single-minded research on the Critical Period hypothesis gave way to realization that recruitment variability was the outcome of complex trophodynamic and physical processes acting over many temporal and spatial scales and throughout pre-recruit life. A complex mix of main effects and interacting factors can easily generate order-ofmagnitude variability in recruitment via small effects on mortality and growth rates during the abundant egg and larval stages, or via cumulative effects during the pre-recruit juvenile stage. New considerations of compensatory mechanisms that can dampen variability and stabilize recruitment emerged. A little density dependence, especially in the relatively long juvenile stage, can regulate recruitment. Multidisciplinary programs instituted in the 1990s and successful development of statistical models and coupled bio-physical models, offered new insights into mechanisms generating recruitment variability. Despite progress, forecasting recruitment remains a formidable challenge. “Solving the recruitment problem” is no longer the Holy Grail of fishery science. Appreciating recruitment variability, explain ing its probable causes, considering implications for management, and understanding it in the context of broader variability in marine ecosystems, are all worthy goals.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Nash, O. S. Kjesbu, E. Trippel, Heidi Finden, A. Geffen
There has been a growing interest in determining the stock reproductive potential (SRP) as a means to better understand the recruitment dynamics of a fish population. The focus in SRP studies has, with a few notable exceptions, been on numbers, maturation and fecundity of females and thereby total egg production (TEP). In the past the SRP of northeast Arctic cod (Gadus morhua) was estimated from TEP over the years 1946 to 2005. In this paper we present estimates of the corresponding total viable sperm production (VSP) based on sperm characteristics from published literature on other cod stocks. There have been large changes in VSP, which to a certain extent reflect changes in the mature biomass of the stock. There was a relatively large variability in the relationship between VSP and TEP in this stock. Since 1946 there have also been changes in mean length of mature males and females with a tendency toward smaller fish in the most recent time period. With the relatively large decline in mean size of mature females and the tendency to mature at a smaller size in the latter years the mature fish of both sexes are now of a similar mean size. The relationship between mean size of mature males and females is substantially different than when the stock was large in the early part of the time series. This could have implications for fertilization success, a factor that is dependent on the dynamics of both sexes in relation to each other. Utilisation of fertilization rates based on the sex ratio and sperm fertilization potential based on the condition of the fish allowed the TEP to be adjusted to an ‘estimate’ of total fertilized eggs, thus including both male and female characteristics in an estimate of SRP. The resulting fertilized egg to recruit plot showed a similar degree of variability as the SSB to recruit plot, however, the pattern was slightly different.
{"title":"Potential Variability in the Paternal Contribution to Stock Reproductive Potential of Northeast Arctic Cod (Gadus morhua)","authors":"R. Nash, O. S. Kjesbu, E. Trippel, Heidi Finden, A. Geffen","doi":"10.2960/J.V41.M619","DOIUrl":"https://doi.org/10.2960/J.V41.M619","url":null,"abstract":"There has been a growing interest in determining the stock reproductive potential (SRP) as a means to better understand the recruitment dynamics of a fish population. The focus in SRP studies has, with a few notable exceptions, been on numbers, maturation and fecundity of females and thereby total egg production (TEP). In the past the SRP of northeast Arctic cod (Gadus morhua) was estimated from TEP over the years 1946 to 2005. In this paper we present estimates of the corresponding total viable sperm production (VSP) based on sperm characteristics from published literature on other cod stocks. There have been large changes in VSP, which to a certain extent reflect changes in the mature biomass of the stock. There was a relatively large variability in the relationship between VSP and TEP in this stock. Since 1946 there have also been changes in mean length of mature males and females with a tendency toward smaller fish in the most recent time period. With the relatively large decline in mean size of mature females and the tendency to mature at a smaller size in the latter years the mature fish of both sexes are now of a similar mean size. The relationship between mean size of mature males and females is substantially different than when the stock was large in the early part of the time series. This could have implications for fertilization success, a factor that is dependent on the dynamics of both sexes in relation to each other. Utilisation of fertilization rates based on the sex ratio and sperm fertilization potential based on the condition of the fish allowed the TEP to be adjusted to an ‘estimate’ of total fertilized eggs, thus including both male and female characteristics in an estimate of SRP. The resulting fertilized egg to recruit plot showed a similar degree of variability as the SSB to recruit plot, however, the pattern was slightly different.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An understanding of the reproductive biology of a species is a central aspect of providing sound scientific advice for fisheries management. Reproductive biology plays a large part in determining productivity and therefore a population’s resiliency to exploitation by fisheries or to perturbation caused by other human activities. This paper provides an overview of variation in reproductive characteristics in commercial fish species and examines the impact on perceived productivity. It is clear that accounting for variation in reproductive biology can have a major impact on advice for fisheries management. Further work is required on the methods used to estimate reproductive characteristics such as maturation, sex ratio, and fecundity, and research to better understand the tradeoffs leading to variation in these reproductive traits. It will also be necessary to demonstrate that incorporating more complex estimates of reproductive potential results in better scientific advice for fisheries manage ment.
{"title":"Integrating Reproductive Biology into Scientific Advice for Fisheries Management","authors":"M. Morgan","doi":"10.2960/J.V41.M615","DOIUrl":"https://doi.org/10.2960/J.V41.M615","url":null,"abstract":"An understanding of the reproductive biology of a species is a central aspect of providing sound scientific advice for fisheries management. Reproductive biology plays a large part in determining productivity and therefore a population’s resiliency to exploitation by fisheries or to perturbation caused by other human activities. This paper provides an overview of variation in reproductive characteristics in commercial fish species and examines the impact on perceived productivity. It is clear that accounting for variation in reproductive biology can have a major impact on advice for fisheries management. Further work is required on the methods used to estimate reproductive characteristics such as maturation, sex ratio, and fecundity, and research to better understand the tradeoffs leading to variation in these reproductive traits. It will also be necessary to demonstrate that incorporating more complex estimates of reproductive potential results in better scientific advice for fisheries manage ment.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2960/J.V41.M615","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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