A length-based population model was constructed for Bristol Bay red king crab, Paralithodes camtschaticus, incorporating stochastic growth, gradual recruitment over length, and a bowl-shaped pattern for instantaneous natural mortality as a function of length. A nonlinear least squares approach was used to estimate abundance, recruitment, and natural mortality. The model was applied to abundance and catch data from 1968 to 1993. The observed population abundances fit well with the model. Natural mortality was estimated to be three to six times higher in the early 1980s than during other periods. High natural mortality coupled with high harvest rates and followed by low spawning biomass may have contributed to the collapse of the population in the early 1980s and its continued lack of recovery. The stock–recruitment data estimated from the length-based model provided a good fit to both general and autocorrelated Ricker models. The general Ricker model is supported by strong recruitment associated with intermediate levels of spawning biomass and extremely low recruitment related to low spawning stock; the autocorrelated Ricker model fit the data slightly better and is supported by the fact that extremely strong and weak recruitment occurred successively over two separate periods.
We examined effects of 5% buffered formalin (2.2% formaldehyde) and 100% anhydrous alcohol on length of larval capelin collected in three samples off Newfoundland. Sample 1 was taken in Trinity Bay during autumn 1984 by oblique tows of bongo nets with 0.33 mm mesh. Larvae were measured live for total (T.L.) and standard length (s.L.), randomly chosen for formalin (n = 1 13) or alcohol (n = 105) preservation, and remeasured after 30min, 1 day, and 6, 12 and 24 weeks. Preserved larvae shrank ( Table I, Fig. I), and profile analysis (Morrison, 1976) revealed that the choice ofpreservative had significant (P < 0,001, d.f. = 4,213) differential effects on both T.L. (F= 28.32) and S.L. (F= 21.41); greater rate and extent of shrinkage occurred in alcohol than in formalin. Significant (P< 0.05) reduction of mean T.L. in alcohol occurred through the full 24 week study, due to both shrinkage and increased fragility and damage to caudal fins of small larvae in alcohol.Sample 2 larvae (n = 1 12), taken by dipnet off the Carbonear dock in Conception Bay during March 1984, measured fresh ( 2 8 4 6 mm T.L.) within 12 h, placed in 95% ethanol for 6 days, transferred to anhydrous alcohol, and remeasured after 12,24 and 36 weeks, shrank less than smaller larvae (sample 1): cumulative percent shrinkages were 4.7,7.2 and 6.6% at 12, 24 and 36 weeks, respectively. There was no significant (t=0.53, P>0.5) shrinkage between 24 and 36 weeks.Sample 3 was collected during spring 1984 by mid-water trawl tows off eastern Newfoundland. Larvae were measured fresh (50-91 mm T.L.) within 1-2 h, washed with TABLE 1. Cumulative mean percent shrinkage of larval capelin from sample I, in terms of total and standard length, when preserved over a period of 24 weeks in alcohol or formalin. Values in parentheses are mean lengths (mm) Range Mean shrinkage (%) Preservative n of fresh lengths (mm) 30 min 1 day 6 weeks 12 weeks 24 weeks Total length Alcohol
Gröger, J. P., Kruse, G. H., and Rohlf, N. 2010. Slave to the rhythm: how large-scale climate cycles trigger herring (Clupea harengus) regeneration in the North Sea. – ICES Journal of Marine Science, 67: 454–465. Understanding the causes of variability in the recruitment of marine fish stocks has been the “holy grail” of fisheries scientists for more than 100 years. Currently, debate is ongoing about the functionality and performance of traditional stock–recruitment functions used during stock assessments. Additionally, the European Commission requires European fishery scientists to apply the ecosystem approach to fisheries in part by integrating environmental knowledge into stock assessments and forecasts. Motivated to understand better the recent years of reproductive failures of commercially valuable North Sea herring, we studied large-scale climate changes in the North Atlantic Ocean and their potential effects on stock regeneration. Applying traffic light plots and time-series (TS) analyses, it was possible not only to explain the most recent reproductive failures, but also to reconstruct the full TS of recruitment from climate cycles, indexed by the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. A prognostic model was developed to provide predictions of herring stock changes several years in advance, allowing recruitment forecasts to be incorporated easily into risk assessments and management strategy evaluations, to promote a sustainable herring fishery in the North Sea. Insights gained from the analysis permit reinterpretation of the sharp decline in the North Sea herring stocks in the 1970s.
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