Length‐Based Reference Points for Data‐Limited Situations: Applications and Restrictions

Abstract

Current fisheries management policies generally require an assessment of stock status, which is a difficult task when population and fisheries data are limited. Three simple metrics based on catch length compositions (i.e., that reflect exclusive take of mature individuals, P mat; that consist primarily of fish of optimal size, the size at which the highest yield from a cohort occurs, P opt; and that demonstrate the conservation of large, mature individuals, P mega) can be used to monitor population status relative to exploitation. The metrics (collectively referred to as Px) were intended to avoid growth and recruitment overfishing, but there was no quantitative linkage to stock status and calculation of future sustainable catches. We attempt to make this connection by exploring the relationship of Px measures to fishing mortality and spawning biomass (SB). The relationships are compared specifically to the current target reference point (0.4 times the virgin, or unfished, SB [SB0]) and limit reference point (0.25SB0) used for the U.S. West Coast groundfish fishery by using simulations based on a deterministic age‐structured population dynamics model. Sensitivity to fishery selectivity, life history traits, and recruitment compensation (steepness) is explored. Each Px measure showed a wide range of possible values depending on fishery selectivity, steepness, and the ratio of the length at maturity (L mat) to the optimal fishing length (L opt). Although the values of Px may be compatible with sustainable fishing, these values are not always sufficient to ensure stock protection from overfishing. Moreover, values for Px cannot be interpreted adequately without knowledge of the selectivity pattern. A new measure, P obj (the sum of P mat, P opt, and P mega), is introduced to distinguish selectivity patterns and construct a decision tree for development of stock status indicators. Heuristic indicator values are presented to demonstrate the utility of this approach. Although several caveats remain, this approach builds on the recommendations of previous literature by giving further guidance related to interpreting catch length composition data under variable fishery conditions without collecting additional information. It also provides a link to developing harvest control rules that inform proactive fisheries management under data‐limited conditions.

Critically Endangered totoaba Totoaba macdonaldi: signs of recovery and potential threats after a population collapse

“…The catch composition also depends on gear selectivity, which has been proposed as an indicator of sustainable catches (Froese 2004, Cope & Punt 2009). How totoaba size structure was affected by bycatch of the sport fishery (hooks) and illegal fishing by poachers (gillnet) was previously unknown.…”

“…These findings pose a potential threat for totoaba since the size at first maturity is 1300 mm in total length (De-Anda-Montañez et al 2013). Thus, neither gear meets the criteria for sustainable catches that avoid exploitation of juveniles and instead focus on mature adults (Froese 2004, Cope & Punt 2009). In the hypothetical case of reopening the totoaba fishery, legalizing either of these 2 methods would involve risks to the totoaba population.…”

“…Fish population reference points based on catch composition of healthy populations elsewhere have been used to avoid the potential threats such as recruitment overfishing and growth overfishing (Froese 2004, Cope & Punt 2009, Vasilakopoulos et al 2011, Brunel & Piet 2013. This information can be used to control the potential threats of different fishing gear to population resilience and conservation management.…”

Model performance for the determination of appropriate harvest levels in the case of data-poor stocks

“…Simpler assessment methods for data-poor and data-limited stocks have been suggested (Froese, 2004;Hilborn, 2003;Kelly and Codling, 2006) and examined (Cope and Punt, 2009) for datapoor situations with limited success. One of the objectives of this study was to examine the advantages of applying a simple or a more complex assessment method when only limited data (indices and length composition data) were available.…”

Indicator-based management recommendations for an artisanal bottom-longline fishery in Costa Rica, Central America

“…With this in mind, a stock assessment is recommended for the fishery's target species, L. guttatus, to identify reference points (Cadima, 2003) as tools for the management of this fishery. Emerging data-poor methods used to analyze fish stocks have included catch data, similar to that collected by researchers in Bejuco, to determine sustainable yields for data-poor fishery resources (Cope & Punt, 2009;MacCall, 2009;Dick & MacCall, 2011). The performance of these target reference points could then be gauged by a management strategy evaluation (Carruthers et al, 2014).…”