The Science Behind FishKit

All the analyses in FishKit are intended to be applied at the spatial scale of a fish stock. A fish stock is an exploited group of fish with some definable attributes which are of interest to fishery managers. As stated in the Glossary, this means that a stock may be a single spawning component, a population, a metapopulation, or comprise portions of these units. For management purposes, stocks are considered discrete units, and each stock can be exploited independently, or catches can be assigned to the stock of origin.

Why is it important to consider the definition of a stock before proceeding with analyses in FishKit? Analyses in FishKit which evaluate the suitability of management measures (e.g., Size Limit Builder and Bag Limit Builder), assume that the management measure under consideration will be applied to the entire stock. Thus, such analyses may not align with reality unless a given management measure is applied to the entirety of the stock. Likewise, evaluations of stock health, as conducted using Stock Health Tracker, function under the assumption that length sampling is representative of the geographic extent of the stock. Thus, apparent sustainability may be misleading unless length sampling is proportionally representative of the entire fish stock and its fisheries.

Is there a practical rule of thumb for defining stock boundaries? While the complex ecology of fish typically necessitates a variety of approaches to comprehend a species’ spatial structure, a practical approach is possible for fisheries practitioners to apply. In practice, Cadrin et al. (2023) suggest that stock boundaries should approximately encompass a fish population (see glossary) to meet conventional stock assessment model assumptions.

What if community-led fishery management does not align with fish stock boundaries? Grass roots approaches to fisheries management sometimes encounter this question. Local actions (e.g., setting a size limit) may only affect a portion of the stock. In this case, analyses in FishKit remain informative about effective courses of action, despite local implementation. That is, a size limit that avoids harvest of juveniles is a good decision regardless of whether only a portion of the fisheries are managed accordingly. Furthermore, the strengths of community-led fisheries management in terms of stakeholder buy-in may outweigh costs of partial jurisdiction in the short-term and perhaps promote momentum for buy-in from neighboring communities in the longer-term.