Size Limit Regulations Research Articles

The Role of Size Limits in Walleye Management

This paper examines the use of size limits in walleye management. It is necessary for the manager to have knowledge of the recruitment, growth, mortality, and structure of the population to make informed decisions regarding minimum, slot, or maximum size limits. Size limits alter the dynamics and structure of the walleye population, and must consider the compensatory responses in the fishery and be site specific to be of optimal value. Underlying considerations for size limit regulations include an intensive enforcement effort—especially in the early stages, hooking mortality, and public education, acceptance and support.

The Effect of a Change in the Size at First Capture in the Rhode Island Inshore Lobster Fishery: A Bioeconomic Analysis

At this time minimum size limit regulations are the primary tool used to manage Rhode Island's American lobster (Homarus americanus) resource. One shortcoming of this policy is its lack of foundation in bioeconomic analysis. To encourage the incorporation of bioeconomic considerations into the management strategy used on this valuable resource, a fishery simulator (Gates 1974) was modified and employed to analyze the effects of changing the size at first capture in Rhode Island's inshore lobster fishery.A cost and earnings survey of Rhode Island's commercial lobster license holders was conducted to provide the economic data required to simulate the fishery. This survey uncovered information characterizing the exploitation of the resource. For example, the survey estimated inshore catch of 2.1 million pounds indicates that three quarters of the inshore catch may go unrecorded. The survey also revealed that full-time commercial harvesters are outnumbered by part-time personnel by a factor of seven, but still land over 90% of Rhode Island's lobster catch.The simulation results also proved quite informative. They suggest that an increase in Rhode Island's minimum size at first capture, if promulgated alone, will not confer increased benefits to society or fishermen. In fact, if a reasonable rate of discount is employed, the analysis indicates the measure will decrease the present value of social surplus generated by Rhode Island's inshore lobster fishery. Averaging over the range of results obtained, an 0.8 mm carapace length increase will reduce annualized benefits by 7%. Alternative larger increases of 1.6 mm and 9.5 mm (3.5 inch minimum) are estimated to bring about 10% and 38% reductions in the annualized value of social surplus that the inshore fishery can be expected to generate. These results are due in part to the substantial short run decreases in catch that the increased minimum sizes generate, and in part because it is assumed that the increased minimum size will govern Rhode Island's landings only.The immediate short run decreases in benefits that accompany the minimum size increases were found to fall primarily on the harvesters of the resource. Averaging over the discount rates employed, 87% of the short run reductions in social surplus subtracted from producer revenues. All results assume that stock recruitment is independent of stock size, that stock reproductive security is not at issue, and that lobster prices are determined in a regional market for live lobsters.Additional simulations were performed to compare the social surplus in the open access fishery with that which might be obtained should access to the fishery be restricted. Also, social surpluses were obtained for the fishery under the assumption that an increased size at first capture results in increased recruitment. These simulations point to the general result that increased harvest selectivity will maximize the sustainable fleet size while concurrently reducing the annual social surplus generated by the fishery.

Spatial Model for an Exploited Shellfish Population, and its Application to the Georges Bank Scallop Fishery

Existing fisheries models employ the "unit stock" concept that makes no explicit allowance for spatial distribution of biomass and effort over a fishing ground. The utility of the unit stock concept rests largely upon the "dynamic pool" assumption. However, this is both invalid for sedentary species, and difficult to apply when information on spatial distribution by statistical subunits is available, as for the Georges Bank (lat. 42°N, long. 67°W) scallop population. By reference to the Georges Bank scallop fishery, more realistic general assumptions for a spatial model of shellfish populations are:a) Recruitment occurs in patches of random size and location with the constraint that local biomass does not exceed the virgin biomass of each unit area.b) The fraction of effort expended within each statistical area of a fishing ground is either determined by available local biomass alone (proportional effort allocation) or in combination with "traditional fishing practice."Therefore, a spatial model (YRAREA) simulating nonrandom recruitment and harvesting of sedentary organisms is postulated and applied to Georges Bank scallop stocks. Some of the general predictions of this model differ significantly from those employing the unit stock concept, as follows:1) Under proportional effort allocation, overall yield declines more sharply with increasing effort subsequent to maximum sustained yield (MSY) than under dynamic pool assumptions. 2) Peak mortality and the apparent point of full recruitment on the catch curve occur progressively earlier in life (even at partially recruited ages) with increased effort or degree of clumping of the population, and subsequently declines with age, except where "fully recruited" ages coincide spatially with the "target" age-group making up the largest biomass component. This may be of general relevance to fisheries under intensive exploitation with sophisticated methods of navigation and fish finding; peak mortality may occur earlier in life than predicted from the gear selection ogive, if year-classes are independently distributed and there is no size limit regulation. 3) Variance in biomass/unit area is predicted to fall with age.For the Georges Bank scallop population, the model described herein predicts that a substantial increase in yield would result from diversion of effort from the Northern Edge to less heavily fished areas of the bank.

Effect of a Size Limit Regulation on the Trout Fishery in Trappers Lake, Colorado

Early studies (1960–63) at Trappers Lake indicated an exploitation of the spawning population of cutthroat trout. A 254 mm size limit was imposed in 1964, and during 1967–68 various aspects of the trout fishery and population were measured to assess effect of the regulation. Statistical analysis of creel census data indicated no significant difference in catch per man hour between years. Neither was there a statistically detectable change in the size structure of the population nor a demonstrable difference between mean spawner age for each year. There was no significant difference between length and weight data for two pre-regulation years. Indications are that the size limit had little, if any, measurable effect on the cutthroat trout population.