A GIS-based approach for managing catch-and-release fisheries

Fishery managers establish limits on the possession of certain sizes or numbers of sportfish to structure populations and manage for sustainability. However, when the vast majority of fish are released, possession limits become less useful for structuring a population because most fish are released alive. I explored a novel approach of coupling environmental modeling with demography and fishery data to determine if environmental habitat capacity influenced abundance in a fishery subjected to differed levels of total annual mortality. Using RAMASGIS (Version 6), I constructed models with data from habitat conditions and twenty years of monitoring (2009-2019) the catch-and-release fishery for Largemouth Bass (Micropterus salmoides) in the upper Chesapeake Bay (Maryland, USA). Abundance in the fishery varied with trends in a key environmental indicator of habitat capacity for the fish, submerged aquatic vegetation, and variation in annual mortality (A). Scenarios with average annual mortality levels for the fishery (A = 38 %) had, on average, 8 % greater abundance than scenarios with the highest annual mortality levels observed for a fishery (A = 46 %). The scenario with the highest annual mortality level required a positive environmental trend in habitat capacity in order to support an abundance similar to that for the average annual mortality scenario. Regardless of the trend in habitat carrying capacity, the proportion of fish at or greater than 381 mm in the population decreased from 56 % (no fishery) to 43 % (average fishing mortality) to 35 % (above average fishing mortality), depending on total annual mortality. Model predictions were supportive of that observed for the fishery in that above average levels of annual mortality and catch were sustained at a period with near or above average habitat availability. However, when habitat declined, catch subsequently became more variable and increased following a period of both lower annual mortality and increasing habitat availability. My results indicate that catch-and-release fisheries should be managed by protecting and improving essential habitat conditions, when possible; and if not, then preventing periodically high levels of annual mortality becomes necessary for maintaining consistent abundance.