|
|
|
|
||
|
|
|
|
|
|
||
The Fluke Controversy
By Bruce Freeman
(from Jersey Coast Anglers Association April 2012 Newsletter) During the past several months, Tom Fote has re-run 11 years of summer flounder (Fluke) articles published in the JCAA newspaper. After reading these, it seems that the only point that can be agreed upon is that any management decision made concerning Fluke will be controversial. Why is this? How can there be so much disagreement between what fishermen see occurring while on the water and what the population dynamic models determine to be necessary in order to maintain the Fluke population at sustainable levels? Surely a species as common to New Jersey and New York waters and as important to both recreational and commercial fishermen as Fluke must have been studied so intensively that we know all the details of its natural history, biological traits, and migratory habits. Surprisingly, this is not the case. While we know many aspects about its natural history and biological traits, there are many more we do not know and this can be part of the problem of the ongoing controversy. But there are other concerns as to the cause of this controversy. Our existing management system is based upon the estimated size of the fish population in question and whether that population is increasing or decreasing. In simplistic terms, biologists take into account all of the variables which are known to influence a fish population and relegate them to a mathematical equation or model. Variables such as the estimated population at some point in time are used together with the numbers that are caught each year by fishermen, both commercial and recreational, as well as the number of fish killed incidentally, but not landed. These last types of mortality are referred to as fishing mortality. Another factor in the mathematical equation is the rate of mortality due to predation, disease, and old age. These are termed natural mortality. Other factors in the equation include the estimated rate of growth which is always occurring in a population, and the amount of newly hatched fish which are entering the population, termed recruits. As can be seen from this simplistic example, some of these variables act to increase the population while others act to decrease it. Once all the variables are determined, the mathematical equation is solved and the answer provided. It is that answer which serves as the basis for the annual quotas. If a model accurately characterizes the fish population in question, the results are a true representation of the status of that fish stock. However, if the model does not accurately characterize the model, the results can be a misrepresentation of the stock and result in a controversy. There are several important conditions that can influence the final mathematical answer or model results. The first is how accurate the estimates are for each of the variables. If they accurately depict the variables, fine, but if they do not, they can consistently produce misleading results. The second condition is the mathematical equation or model itself. Models are being modified and updated all the time as biologists learn more of the complexities and interactions of the variables. As models change, the model results change. An example of this occurred in 2008 when the model being used was changed from the virtual population analysis (VPA) to a forward projecting model (ASAP). This change in addition to a revised natural mortality rate and biological reference points resulted in a substantial change in the Fluke stock status. The third condition is the rate used for natural mortality, a variable that is often difficult to measure. However, a small change to the rate to natural mortality can have considerable influence on the final results. So far as Fluke are concerned, there remain some continuing limitations which underlie basic assumptions used in the model. Unlike most fish populations where we find a direct relationship between the number or weight (biomass) of mature females and the resulting number of young fish being recruited into the population, this does not seem to hold true for Fluke. For example, over the past several years as a biomass of mature females has more than doubled, the number of recruits moving into the population has not increased, but remained about the same. In several cases, the largest number of recruits were produced from a population having a very low female biomass. In addition to this, we find a skewed sex ratio, especially in mature fish. While there is a 1:1 sex ratio in immature Fluke, as they reach maturity within the second or third year of life, females dominate over males and starting by the fourth or fifth year of life, females account for 95-98% of the population. In order to understand the implications of these biological oddities and how they affect the results of population models, JCAA joined with other recreational fishing organizations, commercial fishing organizations, and Rutgers and Cornell universities to form a not-for-profit multi-state multi-institutional partnership named the Partnership for Mid-Atlantic Fisheries Science (PMAFS). The purpose of this partnership is to address the most urgent scientific problems limiting the successful management of fisheries in the mid-Atlantic region. PMAFS is designed to provide the framework enabling these institutions and concerned industry groups to effectively address the most urgent scientific problems in fisheries management and incorporate this critical information into the management process through partnerships with NMFS, the mid-Atlantic Council and the Atlantic States Marine Fisheries Commission. PMAFS requested funding from Congress and with the support of both New Jersey and New York congressional delegations, received them. To date the following studies had been initiated:
As these projects are concluded, we should have much better information to apply to the stock assessment model and hopefully resolve many of the current controversies.
|