NMFS population dynamics Sea Grant graduate fellowship: Modeling the impacts of gear regulations

End Date: 05/31/15


The objective of this proposed fellowship work is to determine the impact of potential gear size regulations on GOM red snapper stock status and recovery. Of particular interest are 1) the effect of different hook sizes on yield per recruit estimates computed by incorporating hookspecific selectivity and discard estimates during both open and closed seasons and 2) the effect of directly-estimated selectivity functions on estimates of maximum sustainable marginal yield (MSMY) and stock recovery projections. Mr. Garner also will evaluate the efficacy of alternative management strategies, such as a “first fish rule,” based on changes in discard levels and the resultant impact to total fishing mortality.


Selectivity and catchability estimates from recently completed and ongoing fishing experiments will be used to determine the effects of regulating hook size on GOM red snapper yield per recruit. Yield per recruit estimates will be computed under three gear regulation scenarios: 1) a no hook size restriction scenario (current regulations), 2) hook size restrictions for each circle hook size tested, and 3) a hook size range scenario restricted between an upper and lower limit of hook sizes examined in completed and ongoing fishing experiments. Yield per recruit estimates under these three scenarios will be compared to YPR estimates under alternative management strategies, such as a “first fish rule,” as well as by varying the minimum size limit. The model of Waters and Huntsman (1986) incorporated the effect of discard mortality into fishing mortality estimates as survival probability (Ps). As survival probability has been shown to be highly dependent on depth (Wilson and Burns 1996), a range of values for Ps
will be explored in the current study using their approach. The specific modeling approach will be adapted from the model derived by Waters and Hunstman (1986) to explore appropriate YPR estimates for red snapper prior to the initial use of minimum length limits in the GOM fishery.


The issue of fishery discards is pervasive, with a minimum of 8% of global catch, or 7.3 million metric tons, being discarded annually (Alverson et al. 1994; Kelleher 2005; NMFS 2011). The true magnitude of global discards is unknown, however, as quantitative discard data are only available for 64% of all fisheries and only 39% of available quantitative records were deemed sufficient for discard analyses (Kelleher 2005). Trawl fisheries consistently yield the highest ratios of discards to landed catch, primarily due to low selectivity of trawling gear and high productivity of target species (Kelleher 2005; NMFS 2011). However, intense effort facilitates nearly as high discarding rates in some hook and line fisheries, where ratios of discarded to landed catch can be as higher than 5:1 during peak fishing seasons (NMFS 2011). Discarded catch, or the portion of the catch returned to the sea, is not the direct problem but rather the mortality associated with releases (Alverson et al. 1994; Davis 2002), which has been estimated to be as high as 100% for physoclistus reef fishes captured at depths greater than ~40m (Wilson and Burns 1996).