Pros and Cons of Pinniped Management Along the North American Coast to Abet Fish Stocks

In this paper, we discuss the merit (or lack, thereof) of controlling pinniped populations for the purpose of enhancing fish stocks. Inherent in this approach is the assumption that predation by pinnipeds limits net production of at least some fish populations and, that any net surplus in production, caused by a culling program, can be effectively utilized in commercial harvests. Four generally accepted ecological relationships work against the success of culling pinniped herds to enhance fishery production. First, prey species almost always have more than one predator. Second, pinniped species rarely are dependent on only one species of prey. Third, the recruitment rate of most fish stocks is highly variable, and this is one of the most likely factors determining stock abundance. And fourth, fish, as a predatory group, consume more fish than do other predators (e.g., seabirds, cetaceans, and pinnipeds). Two examples of control programs and their effects on local fisheries are discussed. The following information is necessary to evaluate the biological merits of a pinniped control program (excluding ethical considerations and public sentiment): (1) kind, size, and amount of target species taken by pinniped species (by age, sex, and area), by other predators, by commercial fisheries, and by recreational fisheries and how knowledge of these takes will be effected by the management program; (2) standing stock, trends in stock size, and the relationship between net production and standing stock of the target species; (3) population size, trends in abundance, status, and net production of pinniped species; (4) expected increase in yield (and confidence levels) resulting from cull, and value of this increase in net production to the fishery and the general public; (5) cost of the control program; (6) proposed number (by age and sex classes) of pinnipeds to be culled each year, and the duration of the cull in years; and, (7) long-term effect of the cull on the pinniped population. It is unlikely that information on points (1), (3), and (4) will ever be known with reasonable confidence. Statistically designed removal experiments may be the only method of determining the merit of a control program. Unfortunately, it will be difficult to generalize results from one such experiment to other areas, species, or fisheries.