The Working Waterfront

Regulators look at increasing lobster reproduction

Larger minimum size considered for Gulf of Maine

Posted 2022-08-09
Last Modified 2022-08-09

There is a great deal of uncertainty facing the lobster fishery. One constant for the last 33 years has been the minimum legal size. Changes to that size are now being discussed.

Addendum 27 (dubbed the “resiliency addendum”) to the Atlantic States Marine Fisheries Commission’s (ASMFC) Interstate Lobster Fishery Management plan considers the future resiliency of the fishery. Although the industry had a record year for value in 2021, all four of the Maine Department of Marine Resources’ monitoring surveys to track the fishery are trending down.

One management measure that could kick in if the fishery were to decline below a predetermined threshold is an increase in the minimum legal size in Lobster Management Area 1 (Gulf of Maine to the Canadian border and out about 50 miles). The current minimum size there is 3-1/4 inches (82.6 mm) carapace length (CL), and the maximum size is 5 inches (127 mm) CL.

It seems climate change has pushed more lobsters to reproduce before they are caught.

Also under consideration for the addendum include changes to the maximum size. Minimum and maximum sizes and V-notch definitions and requirements also are being considered in other management areas. These measures are aimed at increasing reproduction as climate change may depress the lobster stock.

Susie Arnold
Susie Arnold

With all the challenges facing the industry it is difficult to entertain the idea of yet another change, and even more difficult for most to dig into the details behind a proposal. I decided to dig a bit into the minimum size. For simplicity, I’ll stick to coastal Maine, or the National Marine Fisheries statistical areas 511 (Downeast), 512 (Midcoast), and 513 (Southern Maine).

For years, I’ve heard fishermen talk about seeing smaller and smaller lobsters bearing eggs, and numerous studies have demonstrated that warmer water temperature decreases the size of maturity for female lobsters. So just when are lobsters reproducing along the coast, and what proportion reproduce before they are caught?

DMR Senior Lobster Biologist Jesica Waller analyzed size at maturity of female lobsters over three decades and published those results in 2021. For area 511, the size at which 50% of females are mature was 88.6 mm CL, 86.7 mm for area 512, and 83.4 mm for area 513.

These sizes are approximately 6 mm shorter than what was observed in the 1990s.

In contemplating changes to the minimum size, it’s important to consider the current size make-up of legal-size lobsters and the extent to which the smallest legal lobsters are making up the vast majority of the catch. According to DMR commercial sea sampling data from 2016-2021, 97% of legal-size lobsters are between 83-100 mm. Over 100 mm is considered a select lobster by the industry. In fact, 10.6% of the legal catch are lobsters right at the minimum size, 83 mm, with lobsters 83-88 mm making up 53% of the current legal catch.

What is interesting about this is that raising the minimum size only one millimeter could give just over 10% of the current legal catch another year to reproduce. If they don’t reproduce, those lobsters have the potential of growing an average of 9 mm in the next molt so they would be significantly larger when caught as legal lobsters.

We typically think of preserving the largest (because larger lobsters produce exponentially more eggs) as the most important way to protect broodstock, but given that lobsters over 100 mm have made up less than 3% of the catch over the last five years, protecting the smallest females could actually have the highest impact on spawning stock biomass.

There is a lot we still don’t know about how lobsters behave in a warming world. It seems in this way, climate change has pushed more lobsters to reproduce before they are caught.

But is it enough? Are the eggs of these youngsters as viable as those released from larger lobsters? Are the eggs released inshore or offshore finding their way to suitable nursery habitat?

Harvesters have been essential participants in answering these questions, and continued cooperative research between industry, scientists, and managers is the only way to move through these challenging, changing times.

Susie Arnold is a marine scientist with the Island Institute, publisher of The Working Waterfront, working on the impacts of climate change and ocean acidification on marine resources and fisheries-dependent communities. She may be reached at