A Noninvasive Method For In situ Determination of Mating Success in Female American Lobsters (Homarus americanus)

Summary

Fishery-induced changes to exploited crustacean fisheries, such as the American lobster fishery, could potentially influence their reproductive dynamics, leading to a reduction in mating success. This study's goal was to develop a noninvasive method for ascertaining the mating success of female lobsters that may be physiologically or functionally mature.

Abstract

Despite being one of the most productive fisheries in the Northwest Atlantic, much remains unknown about the natural reproductive dynamics of American lobsters. Recent work in exploited crustacean populations (crabs and lobsters) suggests that there are circumstances where mature females are unable to achieve their full reproductive potential due to sperm limitation. To examine this possibility in different regions of the American lobster fishery, a reliable and noninvasive method was developed for sampling large numbers of female lobsters at sea. This method involves inserting a blunt-tipped needle into the female's seminal receptacle to determine the presence or absence of a sperm plug and to withdraw a sample that can be examined for the presence of sperm. A series of control studies were conducted at the dock and in the laboratory to test the reliability of this technique. These efforts entailed sampling 294 female lobsters to confirm that the presence of a sperm plug was a reliable indicator of sperm within the receptacle and thus, mating. This paper details the methodology and the results obtained from a subset of the total females sampled. Of the 230 female lobsters sampled from George's Bank and Cape Ann, MA (size range = 71-145 mm in carapace length), 90.3% were positive for sperm. Potential explanations for the absence of sperm in some females include: immaturity (lack of physiological maturity), breakdown of the sperm plug after being used to fertilize a clutch of eggs, and lack of mating activity. The surveys indicate that this technique for examining the mating success of female lobsters is a reliable proxy that can be used in the field to document reproductive activity in natural populations.

Introduction

American lobster (Homarus americanus) is one of the most productive fisheries in the North Atlantic (~ 56,000 mt in 2011, valued over $390 million)¹. However, there is a general lack of understanding regarding the reproductive dynamics of this species in wild populations. Generating more accurate estimates of reproductive output, including the number and sizes of individuals actively participating in reproduction, may improve the stock assessment process. For example, females that are prevented from achieving their full reproductive potential due to sperm limitation have been identified as a concern for several commercially exploited marine crustac....

Protocol

Part A: Field Sampling Technique

1. Female Measurements

1. For each female lobster, measure the carapace length (CL) and the width of the second abdominal segment to the nearest 1.0 mm using a pair of calipers.
   NOTE: The second abdominal segment is measured because the width of the abdomen (where females carry their eggs) is an indicator of sexual maturity. In addition, it might be advantageous to ascertain the molt stage to later match these data with reproductive stage (see step 1.2).
2. Clip a small distal portion off one of the abdominal pleopods (a standard methodological protocol in lobsters) and store the pleopod in....

Results

The data reported here were for a subset of female lobsters that originated from both nearshore and offshore locations. The nearshore group consisted of 44 lobsters that were captured in the coastal waters near Cape Ann, Massachusetts and transported in coolers to the laboratory for examination. A total of 186 offshore lobsters were captured on George's Bank and sampled at a commercial holding facility in New Hampshire.

Sperm samples were obtained from all of the animals and immediately examin.......

Discussion

This video and paper outline and demonstrate a method for determining if female lobsters have successfully mated. This approach is simple enough that it can be used for large-scale sampling of lobsters at sea by a variety of users. The method is based on detecting the presence of a spermatophore in the seminal receptacle that is passed from male to female lobsters during mating. These spermatophores partially harden into a sperm plug shortly after they are deposited in the receptacle; thus, the presence of a sperm plug i.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Calipers	Mitutoyo Digimatic	500-196-20	http://www.globalindustrial.com
3 ml Luer-Lok syringe	Beckton-Dickinson	309585	www.bd.com
Monoject aluminum hub blunt needles, 18 G x 1	Webster Veterinary	8881202348	www.mywebstervet.com
2.0 ml Plastic storage tubes	Eppendorf	wu-06333-72	http://www.coleparmer.com
Styrofoam cooler with ice
Compound light microscope	Olympus	BH System	http://www.olympusamerica.com
Glass sides with cover slip			75 mm x 25 mm, ~1 mm thickness
Pipettor with disposable tips