To Catch a Scallop

December 21, 2010 09:57

In Quebec, the great majority of scallops are harvested along the coast of the St. Lawrence, across from Havre-Saint-Pierre and south of the Magdalen Islands. Living at the bottom of the ocean in groups, which are referred to as scallop beds, these molluscs are found on rock, gravel or shell substrates. Their movements are quite limited. Fishers know the locations of these scallop beds quite well, returning to them every year when the season opens, reports with reference to Fisheries and Oceans Canada.

But how do we ensure that this resource doesn't get depleted? That's the responsibility of the Department of Fisheries and Oceans (DFO). Biologist Hugo Bourdages at the Maurice Lamontagne Institute in Mont-Joli Quebec is working on it. He produces a scientific report assessing scallop stocks in Quebec every three years. His assessment of stocks and of different control measures has helped ensure stable scallop populations in these main harvesting zones. Two scallop species are found in Quebec waters: Atlantic sea scallops and Icelandic scallops. This article focuses specifically on the Atlantic sea scallops harvested around the Magdalen Islands.

The commercial scallop fishery took off in Quebec in the mid-1960s. Predictably, scallop stocks declined after the resource was exploited for the first few years. Over time, however, Fisheries and Oceans Canada established a number of control measures to help replenish and maintain the stocks. In particular, harvesting was reduced by imposing quotas or fishing days in the most critical areas. In the Magdalen Islands, fishers are each entitled to 15 fishing days per season. During these authorized fishing days, they have no restrictions on the volume they harvest. However, the number of hours at sea is rigorously controlled and each fishing vessel must be equipped with a satellite positioning device.

Modifications to fishing gear are another form of control measure. Scallops are harvested with a dredge, which looks more or less like a basket that is dragged along the seabed. A series of these dredge bags are used to capture scallops (see Figure 1). The size of the rings in the dredge bags is regulated to ensure that only scallops with a shell size larger than the minimum 95 mm (in the case of sea scallops) remain in the bags. Scallops of this minimum size are generally five to six years of age. Although scallops can live more than 20 years, they achieve their maximum growth around the age of six years. Between their fifth and sixth year of life, the meat weight of a sea scallop can increase from nine to 13 grams. Since the market value of scallops is determined by meat weight, it is to the advantage of fishers to leave smaller specimens in the water.

However, the minimum catch size for Atlantic sea scallops is being called into question, with a view to increasing reproduction of the species. DFO is considering increasing the ring size of dredge bags from 95 to 100 mm. It would not be the first time that such an increase was imposed: ring size has already been increased from 85 mm to 90 mm and, subsequently, from 90 mm to 95 mm. For fishers, increasing the minimum catch size would mean leaving scallops in the water for an additional year. The benefit to doing so would be in the larger scallops harvested. From a physiological standpoint, this additional year of life for scallops would increase their production of gametes. Scallops reproduce in water by releasing gametes, which are fertilized: the microscopic eggs released by females are fertilized by sperm released by males. The release of more gametes will thus improve the rate of successful reproduction and increase the size of the next generation of scallops. Fishers are actively involved in reviewing control measures. In particular, they participate in research projects at sea that use dredge gear with rings of different diameters. The idea is to develop dredge gear that will minimize catches of scallops under the legal limit.

In addition to minimum catch sizes and control over the fishing process, it is necessary to know how efficiently authorized fishing gear works. What percentage of the scallops in beds are actually caught when fishers dredge the ocean bottom? The efficiency of scallop dredge gear has been a question of particular interest to DFO Science Sector experts. Studies conducted on the subject since the 1970s have placed dredge gear efficiency at between 10% and 20%, meaning that only about one in five scallops is caught on any given haul. This low fishing gear success rate led to the belief that the resource could not be over-exploited. However, more recent studies have cast a measure of doubt on those results, indicating that dredge gear is in fact far more efficient than originally believed. To clarify the situation and adjust its regulations accordingly, DFO conducted a research project to test various dredge gear efficiency assessment methods.

Researchers used data from the commercial fishery, namely fishers' own logbooks, as well as records of landings and independent at-sea sampling programs. They also did experimental fishing using the same dredge gear as the fishers and specially designed software. The results were surprising: dredge gear efficiency is substantially higher (40% to 70%) than what had been estimated 30 years ago. When fishers dredge over a bed of scallops, they catch about half of them. The yardstick that fisheries management depended on has changed dramatically! It's precisely this type of data that biologist Hugo Bourdages uses to form the scientific advice he gives to those managing the fishery.

The advancement in knowledge achieved through research projects and the adaptation of fisheries management tools therefore make it possible to closely monitor the state of the resource, preserve it, and ensure that fishers will be harvesting scallops well into the future.

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