Scale Matching:
By Rebecca Martone    Awards: Haderlie, Myers, Miller

Worldwide, management efforts are failing to reduce overexploitation of fisheries populations. This is due, in part, to routine oversight of the spatial variability in the life history traits (e.g. growth rates, reproductive output) of the species they are trying to protect. Most fisheries management models include the assumption that the coastal ocean is a well-mixed and fairly uniform environment, despite considerable evidence to the contrary. Many marine species, especially invertebrates like abalone or marine snails, are distributed in patches across the ocean, where distinct populations are relatively independent of other populations. As a result of this distribution in space, local populations may be overexploited if most of the individuals are removed from a few populations and these populations are not replenished. For example, in Tasmania fishers were targeting abalone populations close to port, and as a result, most of the individuals were removed close to shore. This led to a decline in the overall numbers of abalone in the region and eventually fishery closures. In response, fishery managers and industry members applied rules in which only a proportion of the individuals from each distinct population could be removed and now abalone populations and even fisheries production levels have increased, whilst almost every other wild fishery industry has seen declines.

As part of the Baja Biocomplexity Project, an interdisciplinary collaboration between several U.S. and Mexican institutions studying a unique group of fishing cooperatives on the Pacific coast of Baja California Sur, I am exploring spatial patterns of reproduction and growth of Megastraea undosa, a fished marine snail. These fishing cooperatives are granted exclusive fishing rights to several invertebrate species, including M. undosa.

This system of management allows each cooperative to set quotas for their region and all cooperatives enforce identical management measures, including a seasonal closure (from November to May) and a minimum legal size of 90 mm in basal diameter. However, the cooperatives are located along a peninsula that experiences a range of oceanographic conditions, and thus may be fishing populations of snails that have different life history traits, important things to consider when setting fishing quotas and size limits. In the North, areas of persistent upwelling are dominated by cold nutrient rich water and maintain high biomass of high quality macroalgae, the primary food source for M. undosa, while in the South areas of less upwelling and lower nutrient inputs are characterized by warmer water and reduced macroalgal abundance and quality. Since both temperatures and food availability can affect individual growth and reproduction, this abrupt shift in environmental conditions may lead to geographic differences in the growth and reproduction in populations of this snail. I am exploring if there are differences in the life history traits of M.undosa populations across these different oceanographic conditions using a combination of tagging studies, reproductive measurements, isotope studies and underwater surveys, and asking whether area-specific management measures such as size limits and quotas should be applied. So far we have found that populations in regions under different cooperatives do have different growth rates and reproductive potential, and we are working with the cooperatives to improve management measures for this species.