Fishery implications of smaller asymptotic body size: Insights from fish in an extreme environment

The asymptotic body size of fish species is particularly vulnerable to changes in environmental conditions, such as salinity, temperature, and food availability. One critical fisheries implication of this response is changes in yield; notably, yield reduction is expected to result from species with smaller asymptotic sizes. However, changes in asymptotic lengths are associated with changes in other vital rates as well—including growth coefficient and natural mortality—which also affect fishery yields. Here, we investigate the effects of smaller asymptotic lengths—and associated vital rates—on fisheries yield-per-recruit by comparing fish species occurring in one of the world’s most extreme marine environments, the Arabian/Persian Gulf (Gulf), with their counterparts in the adjacent and more environmentally benign Oman Sea. By comparing seven species in the two areas, we find that most species occurring in the Gulf consistently attain smaller asymptotic lengths than those in Oman Sea—an outcome that is consistent with the finding that species living in environmental extremes attain smaller body sizes. While the majority of species attaining smaller asymptotic lengths occur in the Gulf, more grew faster towards their asymptotic lengths and it is expected that these fish have higher natural mortality. When examining fishery implications by setting vital rates based on area, smaller asymptotic lengths did not necessarily result in a lower yield-per-recruit, particularly in species with small differences in asymptotic sizes and higher growth coefficient and/or lower natural mortality. Our results suggest that a more nuanced evaluation of the fishery impacts of smaller asymptotic body sizes can be obtained by accounting for vital rates in addition to asymptotic fish sizes.