Evaluating Localized vs. Large-scale Management: The Example of Tautog in Virginia

Abstract

Choice of management spatial scale is a critical step of any stock assessment, but deciding on a conservative criterion is difficult because of risks associated with any choice. For example, if one large unit is selected when distinct sub‐stocks exist, then some population components may disappear over time. Alternatively, choosing several small management units when one well‐mixed stock exists may lead to costly and ineffective management. We consider the example of tautog (Tautoga onitis). Mortality estimated for a single stock using virtual population analysis has exceeded the target and resulted in mandated reductions in fishing. In Virginia, tag returns and catch curve analyses are consistent with a localized mortality rate that is less than the target. Therefore, reductions of fishing effort in Virginia may not alleviate overfishing elsewhere and might not be conservative. Thus, simple models used for localized assessment can have advantages over sophisticated models applied to an entire stock complex when multiple stocks exist.

Size variation of the common whelk, Buccinum undatum, over large and small spatial scales: Potential implications for micro-management within the fishery

“…The authors concluded that if an area was managed on a large-scale, such as the EU minimum landing size for B. undatum of 45 mm, but the area consisted of several sub-stocks which showed real biological differences in terms of population parameters, potential management problems would arise. Such problems would include the inability to detect local stock depletion, and a potential loss of genetic diversity and yield (Tuckey et al, 2007). This study has shown that there is potential for such micro-management measures in Shetland but further research should be conducted examining spatial variation of growth rates and size at maturity in B. undatum before such plans could be developed.…”

“…However, such measures would have to be reviewed on a region by region basis to assess their practicality. Tuckey et al (2007) evaluated the advantages and disadvantages of large-scale and small-scale (localised) management schemes. The authors concluded that if an area was managed on a large-scale, such as the EU minimum landing size for B. undatum of 45 mm, but the area consisted of several sub-stocks which showed real biological differences in terms of population parameters, potential management problems would arise.…”

Recommendations for Catch‐Curve Analysis

“…Graphical depiction of catch-curve data can reveal violations of the assumptions. Tuckey et al (2007) discussed the situation in which mortality changes over time or across ages. Jensen (1984) discussed the problem of heterogeneous mortality rates among subpopulations.…”

An individual-based approach to year-class strength estimation

“…For fisheries-independent surveys that are repeated over multiple years, year-classes may be observed at several ages and analysed separately (Pope, 1972;Ricker, 1975;Serns, 1986). This approach to year-class strength estimation is referred to as the cohort method (Tetzlaff et al, 2011) or the longitudinal catchcurve method (Tuckey et al, 2007).…”