The proportion of mature fish at age or length is one of the most important population attributes in assessing reproductive potential. This proportion is usually named the maturity ogive. The most crucial step in estimating this proportion deals with maturity staging assessed by macroscopic or histology analysis. Macroscopic analysis is relatively inexpensive but usually introduces large amount of error. Histology is the most accurate method for maturity staging but is expensive and time consuming. Here, we propose using the gonadosomatic index (GSI) as an alternative way to estimate the maturity ogives. A logistic multinomial model was implemented to separate immature, mature-active, and mature-inactive fish, based only on their value of GSI. We evaluated the performance of the GSI-based method by comparing the results with ogives estimated from macroscopic and histological staging using the extensive database available for Chilean hake (Merluccius gayi gayi). Maturity ogives from GSI analysis were evaluated at the start and end of the reproductive season. Results showed that, in all cases analysed, maturity ogives from GSI were closer to the ogives based on histology than those from macroscopic staging. Comparing across periods, those maturity ogives computed at the start of the reproductive season give estimates very similar to those from histological staging. To have unbiased estimates of maturity ogives from GSI analysis, we recommend using data from the start of the reproductive season to minimise the frequency of spent fish. In addition, the assumption of the isometry between gonad and gutted weight across maturity stages needs to be tested before the use of this GSI method. The analyses presented here provide a promising method to estimate maturity ogives when histological staging data are lacking or when macroscopic analysis is suspected to have large amounts of errors.
In Chile, bottom trawling for squat lobsters is one of the most important crustacean fisheries. The fishery has been monitored for the past 15 years to assess the resource status, spatial distribution and effects on benthic species. Understanding the interactions of fishing and non-fishing activities with the benthic communities is of critical importance to estimate the potential bycatch of important economic species from fishing operations and to determine adequate spatial and temporal fishing bans. In this study we characterised the community of the main non-target species caught during historical squat lobster biomass surveys from 2000 to 2015 and interpreted the species included as potential bycatch of the fishery. Four ecological assemblages were found that differed in abundance but not in species richness, which suggests that the community structures did not differ among the areas, but rather in the relative abundances of the species. In addition, we created habitat suitability maps for the groups identified and discuss the effects of the environment and the survey method on the distribution of the groups. Managers can use this information to detect regions with high bycatch risk for demersal trawl fisheries and understand the potential interaction of fishing operations with the environment.
Summary
This study examines the seasonal variability in gillnet size selectivity for the main Chilean hake (Merluccius gayi gayi) fishery off the coast of central Chile. Selectivity estimates were based on five gillnet mesh sizes (50, 60, 70, 80, 90 mm) in four traditional fishing areas, and during periods of low and high reproductive activity. Average fish length caught in the earlier period (low reproductive activity) was 30.8 cm LT (±4.17), and significantly longer (p < .05) at 35.9 cm TL (±6.15) in the latter period (high reproductive activity). For males, the selectivity factor was similar in both periods, thus the estimated modal lengths did not differ seasonally (p > .05). For females, however, both the selectivity factor and the estimated modal lengths changed significantly depending on the time of year (p < .05). A significant increment was estimated in the girth/perimeter ratio and condition factor during the period of higher reproductive activity. This change in the fish girth of females during spawning helps explain the significant reduction in their selectivity factor estimates in August–October.
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