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by Madeleine Hall-Arber
NEW BEDFORD, MA - The University of Massachusetts Dartmouth School of Marine Science and Technology (SMAST) hired former commercial fisherman Bob MacKinnon to broadly distribute cod tagging kits, train fishermen to use them, and increase publicity to encourage tag returns.
This project is focused on the broad range of cod movement, hoping to identify migration routes and environmental preferences.
Since August 2000, commercial fishermen of all gear types, party boat captains, and personnel onboard Massachusetts and Maine state fisheries boats have participated.
Commercial fishermen are asked to tag "surplus fish" - that is, any fish over the 400-pound limit, which they have to discard - during the course of routine fishing trips.
The project offers fishermen $2 for each fish they tag. Those who return the tags receive a "Cod-tagging Project" hat.
At a minimum, fishermen are urged to record the location and date tagged and measure the length of the fish. Fishermen who recover tagged fish are encouraged to make a note of what gear they used to catch the fish.
MacKinnon, who has been working alone since his colleague David Martin left for Alaska last July, travels up and down the coast of Massachusetts teaching fishermen how to use a tagging gun to insert standard yellow "spaghetti" tags into fish.
Dr. Frank Bub, an oceanographer supervising the SMAST project, explained that fish markets often find and report the tags when they cut fish, so MacKinnon also has to find the vessel that sold the fish to the market and talk to the fishermen to learn where they were fishing on the day the fish was caught.
12,000 fish tagged
By December 2001, MacKinnon and 80 participating fishermen had tagged 12,000 fish.
However, only 300 returns (2.5%) had been catalogued. One theory is that the small percentage of returns may illustrate the increased availability of cod, which makes it harder for fishermen and buyers to notice the tags.
The SMAST group also tagged 105 fish with green tags that record pressure at depth and temperature. Sixteen of these tags (16%) had been returned, a remarkable return rate compared to the yellow tags.
The pressure-temperature tags are inserted into larger fish, making the survival of both the fish and the tags more likely, thus possibly explaining the higher return rate.
However, these instruments are much more sensitive than the markers and must be handled more carefully. For example, one of the tags was left on a truck's dashboard for a few weeks and half-a-year's data was lost, probably due to the car radio's magnetism.
Finally, four cod were tagged with pressure-temperature-salinity tags. Of those, one has already been returned.
Several results are indicated by the returns so far. It is clear that big fish travel further than small fish. The same small fish have been caught over and over again in lobster pots.
Also, when the water warms up too much, the fish take off for deeper water. They seem to consistently choose 3°-5°C (40°F) water.
What is not yet clear is any discernible pattern of the movement. Researchers have noted a straight-line movement between Humarock and Nauset, but, otherwise, the fish seem to move in all directions.
Some "hang out" where they are tagged, others "zoom," MacKinnon said. Others move along, but slowly.
With sufficient tag returns, graphs of where the fish were tagged and where they traveled might show some interesting patterns.
One indication of this is the track of a cod bearing one of the pressure-temperature tags. Tagged on Stellwagen Bank, the fish moved down to the Great South Channel. The tag data allowed the scientists to trace the depth and temperature contours in between.
Another fish traveled from Scituate to Portland, ME and a few moved around Provincetown and headed south. There are rumors of a tag found near Sable Island, but the tag had not yet been returned.
According to Bub, statistical analyses were being done to find out how the pressure-temperature data relates to tides and "internal waves."
He noted that the pressure data measures tides nicely and, so far, supports what fishermen know - specifically that cod usually stay near the bottom. Occasionally, however, a cod will pop up in the water column.
While there is insufficient data recorded to make broad generalizations, the fishermen contacted about the project have had some surprising observations to relate.
One found a haddock in the Great South Channel. A lobsterman out of Nahant found 22 cod in a single trap and 13 in another. Many noted that they are seeing large numbers of cod inshore.
SMAST tagging project principals David Martin, above left, and Bob MacKinnon, holding fish, put in sea time showing fishermen the technique involved in cod tagging, measuring, and releasing. In addition to the standard yellow spaghetti tag, some cod received tags capable of measuring pressure and temperature. Lacking in the project, so far, have been tag returns. Fishermen catching tagged cod are asked to provide basic information about where and how they caught the fish.
Measure of success
One of the major goals of this project is to involve fishermen in the scientific process, a goal that has already been met. Additionally, the information on cod movement, especially as it relates to depth and temperature, will help contribute to understanding about fish biology and ecology.
Funding is an issue for the continuation of this project. Bub would like to see the project expanded and additional data collected, but since it is relying on Massachusetts state funding - and the state budget is currently uncertain - new directions are in limbo.
SMAST has access to 1,000 additional pressure-temperature tags, but since they were originally developed for freshwater fish, protective casings will have to be fabricated for use on deep-diving cod. A company has been identified that can construct the casings once funding is secured.
Where are the tags?
Of concern to project participants is the low number of tag returns.
Given the 400-pound limit and the price differential between scrod and market cod, the chances are much greater that fishermen are keeping only large cod and, at this point, returning only those tags.
Furthermore, commercial fishermen cannot go into the closed areas and recreational fishermen may not be able to catch larger cod on their lines.
Prey-predator interactions may also account for some of the missing tags. Dogfish evidently ate one of the tagged fish, leaving only the tag and portion of the fish entwined in a gillnet.
Finally, more than a few fishermen apparently assume that any information gained from the tags will be used to close areas to commercial fishing. Some freely admit that they ignore any tags they see.
Fishermen south of the 42° line, in particular, are wary of reporting tag returns out of fear that the data will be used to show that the stocks mix sufficiently to prompt tighter quotas in the southern portion of the region.
At least one recreational fisherman refused to return tag information unless the cost of his phone call was reimbursed.
The fishermen who are involved in these tagging projects, however, believe that it is important to undertake the science and learn.
"Science is not sleight of hand. It is not a conspiracy to get rid of fishermen," said New Hampshire fisherman Dave Goethel. "Besides, we who complained the loudest (about management) have to be willing to be part of the solution."
