Unknown Life History of the Channeled Whelk

The unknown life history characteristics of the channeled whelk

By Steve Wilcox*

This article summarizes Mr. Steve Wilcox MS dissertation work under the direction of Professor Kenneth Oliveira**, UMass Dartmouth

channeled whelkAn Overview: Drastic declines in the lobster landings as well as reductions in other trap caught species have increased pressure on the channeled whelk (Busycotypus canaliculatus) in Southern Massachusetts.  The need for affected fishermen to supplement their income and the relative easy transition of their boats and gear to the whelk fishery has lead to the rapid development of this fishery. 

Channeled whelk, which was once only caught as a bycatch in lobster traps, is now a directed fishery that produces over 2.5 million pounds per year in Southern Massachusetts.  Landings from Nantucket Sound, Martha’s Vineyard Sound and Buzzard’s Bay account for more than 90% of state trap landings for channeled whelk.  Currently, there is extremely limited information about the age structure, growth rate, size at maturity, and population variation within these areas.  Now that an increased number of fishermen rely on this resource as a significant portion of their income, it is vital that this information be gathered.  Life history strategies need to be understood to produce a viable stock assessment that will allow for meaningful management to the fishery within each of these three areas.

The Study: Samples will be collected from Nantucket Sound, Martha’s Vineyard Sound, Buzzard’s Bay, as well as an area closed to fishing.  Samples will be collected using a standard whelk trap fished with in the designated areas.  We will examine and compare population age structure, size, weight, sex and determine if the animal is sexually mature in each area.  Additionally we will look into seasonal changes in weight and reproductive potential to examine if there is an optimal harvest time which would allow for additional reproduction while minimizing loss in current levels of annual landings.

Data generated from this project will be used to aid in management of the channeled whelk fishery.  Information for the size and age structure as well as the size at maturity for each stock area will be directly used in stock assessments.  Knowledge of life history coupled with better understanding of seasonal changes in weight and reproductive condition may lead to a management plan that could increase reproduction output of the stock and maintain the long term sustainability of annual catch.  The ultimate goal of this project is to develop a much better understanding of the biology of this species and to better inform the management process.

The Fishery

Massachusetts current regulations for the channeled whelk fishery are a minimum legal size of 2 ¾ (70 mm)” shell diameter and a 200 trap limit per fishermen.  There is also a closed season from December 15 thru April 14 each year.  The channeled whelk fishery has a limited license entry and licenses can not currently be transferred.  Massachusetts currently issues 155 permits per year of which roughly 2/3 are have been actively fished at some point during the year.  However in recent years there has been a trend of increased effort amongst active fishermen.  Landings are at a time series high (Figure 1).  However, fisheries independent data collected from the Massachusetts Division of Marine Fisheries (MADMF) show mean abundance to be at a 30 year time series low (Figure 2).

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Figure 1.  Annual Massachusetts channeled whelk landings showing recent years at time series highs.

Often minimum legal sizes are designed to allow for a portion of the females to reproduce prior to harvest.  In the case of the channeled whelk, the size at which the females begin to reproduce, and whether it is the same across all areas is as of yet unknown.  The minimum legal size seems to have been developed by the processors that buy the catch.  The closed season that is in place coincided with a seasonal period of dormancy that the channeled whelk goes through due to low water temperatures.  This reinforces the importance of determining whether males and females are utilizing the same life history strategies, what size and age they are maturing at, whether this is uniform across all areas, and what effects fishing may be having on this species.

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Figure 2.  Loess smoothed curve from MADMF trawl survey showing downward trend in mean abundance of channeled whelk.

Answering Current Unknowns

To gain a better knowledge of the biology of the local channeled whelk specifically in Buzzard’s Bay, Martha’s Vineyard Sound, and Nantucket Sound, samples will be harvested from each area.  Basic biological characteristics will be obtained through investigation of the following life history parameters:  external shell dimensions, age (determined from growth rings on operculum), whole weight, characterization of sex (presence of a penis or a nidamental gland) (Figure 3), weight without shell, mass of gonads, as well as confirming maturity by presence or absence of sperm or eggs (Figure 3).  We will compare the biological characteristics from animals collected in an area closed to fishing with animals collected in an open area.  This will allow the unique ability to look at a stock of animals that has no human removal, and compare it to animals from an area where harvest is occurring.  Monthly samples will be taken from Nantucket Sound and Buzzard’s Bay.  These samples will be used to monitor gonad weights and help pinpoint the time of year when reproduction is occur for both sexes. 

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Figure 3.  Left – a male channeled whelk showing penis and gonad, Right – a female channeled whelk showing gonad with eggs and the nidamental gland.

To confirm that maturity is being determined correctly we will make gonad weight indexes and look for the width of the whelk at which gonad weight rapidly increases to determine the size and age at maturity ogives, or cumulative line graphs, will be made for both genders in all areas.  This will plot the age of the animal against the proportion mature and determine the age at which most animals are maturing.  This will determine if both genders have the same or are utilizing a different life history strategy.  By determining the size and age at which channeled whelk are maturing and whether or not it is the same for all areas we will be able to determine if one fisheries management strategy is sufficient.  The information that we come up with will be presented to fisheries managers with the goal of developing a sustainable fisheries management plan, assuring the long term well being of both the channeled whelk resource, and the fishermen.

Contact information: *Mr. Steve Wilcox Steve.Wilcox@state.ma.us, Professor **Kenneth Oliveira koliveira@umassd.edu; visit Dr. Oliveira WebLink (click on it).



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