Rethinking length-based fisheries regulations: the value of protecting old and large fish


Recently I coauthored a paper in the journal Fish and Fisheries comparing the relative performance of harvest slots verses minimum-length limits as policies for regulating recreational fisheries.  The paper is in response to the paucity of evaluations of harvest-slot regulations and the apparent default use of minimum-length limits to prevent overfishing.  The aim is to proFaF_figvide general guidance to managers of a range of recreational fisheries.  The novelty of the paper is that we evaluated the performance of harvest slots in terms of multiple fisheries and conservation metrics, across a range of fish life-history strategies, for moderate and high-effort fisheries, and across a range of fisheries objectives. Full text copy can be downloaded by clicking here.

Abstract: Management using length-based harvest regulations is common, but such policies often create trade-offs among conservation (e.g., maintaining natural age structure or spawning stock biomass) and fishery objectives (e.g., maximizing yield vs. catch of trophy fish). By focusing harvest on the larger (older) fish, minimum-length limits are thought to maximize biomass yield, but at the potential cost of severe age and size truncation at high fishing mortality. Harvest slot-length limits (harvest slots) restrict harvest to intermediate lengths (ages), which may contribute to maintaining high harvest numbers and a more natural age structure. However, an evaluation of minimum-length limits vs. harvest slots for jointly meeting fisheries and conservation objectives across a range of fish life-history strategies is currently lacking. We present a general age- and size-structured population model calibrated to several recreationally important fish species. Harvest slots and minimum-length limits were both effective at compromising between yield, numbers harvested and catch of trophy fish while conserving reproductive biomass. However, harvest slots consistently produced greater numbers of fish harvested and greater catches of trophy fish while conserving reproductive biomass and a more natural population age structure.  Additionally, harvest slots resulted in less waste in the presence of hooking mortality.  Our results held across a range of exploitation rates, life-history strategies, and fisheries objectives.  Overall, we found harvest slots to represent a valuable option to meet both conservation and recreational fisheries objectives. Given the ubiquitous benefits of harvest slots across all life-histories modeled, rethinking the widespread use of minimum-length limit is warranted.

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