The use and performance of survey-based pre-recruit abundance indices for possible inclusion in stock assessments of coastal-dependent species

Abstract

We reviewed the use of survey-based pre-recruit abundance indices in short-term recruitment forecasts for fish species relying on coastal habitats at the juvenile stage and that are assessed by ICES. We collated information from stock assessment reports and from a questionnaire filled out by the stock assessors. Among the 78 stocks with juvenile coastal dependence, 49 use short-term forecasts in stock assessment. Survey-based pre-recruit abundance indices were available for 35 of these stocks, but only 14 were used to forecast recruitment. The questionnaire indicated that the limited use of survey-based pre-recruit abundance indices was primarily due to sampling inefficiency, which may preclude reliable recruitment estimates. The sampling is inefficient because the juvenile coastal distribution is outside the geographical area covered by large-scale surveys or targeted coastal surveys are conducted on limited spatial and temporal scales. However, our analysis of the relationship between survey-based pre-recruit indices and assessment-generated recruitment indices revealed that survey-based pre-recruit abundance indices were sufficiently accurate to provide useful information for predicting future recruitment. We recommend expansion of the use of survey-based indices of pre-recruit abundance in stock assessment and recruitment forecasting, and consideration of how to include juveniles in ongoing and future surveys.

Spatiotemporal patterns of variability in the abundance and distribution of winter-spawned pelagic juvenile rockfish in the California Current

“…Although we cannot be certain that our survey would have recognized the strength of this year class had the spatial footprint been broader, the observation that high numbers of YOY were observed in power plan impingement and submersible surveys in southern California [15,56] and in scuba surveys in northern California [30] for this year suggests that this would have been the case. Regardless, our results confirm that spatial and temporal patchiness are clearly a challenge to successful evaluation and enumeration of pre-recruits and subsequent development of effective pre-recruit indices for stock assessments, as has been previously observed in other comparable survey programs [20,21].…”

“…Other studies have shown that pre-recruit indices can provide robust information for informing future recruitment and cohort strength, even when such indices are based on surveys that do not completely overlap the spatial extent of the spawning stock [ 20 , 21 ]. These studies have also found that forecasting tends to be more robust with later life-history stages (e.g., pelagic juvenile indices tend to outperform egg or larval indices), and that indices may be enhanced by combining empirical abundance data with environmental data [ 20 ].…”

“…When strong year classes do occur, they can later lead to short-term spikes in catch rates of smaller, younger individuals, potentially complicating quota-based management efforts if the increased availability to fisheries is not forecast by the stock assessment models that inform management. Monitoring the abundance and distribution of juveniles can provide recruitment indices to inform stock assessment models, by providing data on the relative magnitude of incoming year classes subsequent to the larval and late-larval stages during which most density-independent mortality takes place [ 6 , 20 , 21 ].…”

Diverse integrated ecosystem approach overcomes pandemic-related fisheries monitoring challenges

“…For stock assessments, abundance estimates of pelagic YOY are developed from survey data and are used as an index of year class strength for a number of commercially and recreationally important groundfish in the West Coast fishery (see PFMC in “Data Availability”). As groundfish species experience considerable variability in cohort strength from year to year, with the difference often spanning several orders of magnitude 40 and typically being weakly related to spawner abundance 41 , the intent of the survey indices is to improve model forecasts of the abundance and availability of these year classes to commercial and recreational fisheries 36 , 42 , 43 . In doing so, continuous time series are of the greatest utility, as the objective is to ensure that strong year classes that might substantially alter population trajectories are recognized prior to entering the fisheries.…”

Adapting Simple Index-Based Catch Rules for Data-Limited Stocks to Short-Lived Fish Stocks’ Characteristics

“…The full-population advice calendar, in which the abundance index provides information on all exploited age classes over the entire management year, as for instance when a pre-recruit survey index is available, entailed further improvements with respect to the other management calendars. Early indication of recruitment strength have already been demonstrated to be beneficial in other works (Dichmont et al, 2006a;Le Pape et al, 2020). However, the improvement over the in-year procedure was smaller than that between the interim and the in-year advice procedures.…”