Date of Award

12-2011

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Yong Chen

Second Committee Member

Graham D. Sherwood

Third Committee Member

Jonathan H. Grabowski

Abstract

The American lobster (Homarus americanus) is one of the most economically important species in the USA, with most landings from the coastal waters in the Gulf of Maine. In recent years lobster stock abundance has exponentially increased in the Gulf of Maine. Many factors can influence lobster life history that may contribute to the present state of lobster populations in the Gulf of Maine including temperature and predation. As an overture for analyzing growth and temperature from an 18-year juvenile lobster mark-recapture time series in which coded micro wire tags were used, I evaluated tagging by coded micro wire tags for juvenile American lobsters in a controlled study to determine tag retention and any influence on growth increment, intermolt duration, and survival. I found that tag retention rates were high, and tagging did not influence growth or survival (P > 0.05). Therefore the field data procured from this method should not be biased by tag related artifacts. From the mark recapture data set I calculated relative growth (as a percentage of size), intermolt interval, molt incidence, and molt probability in relation to both time at large and cumulative degree days-at-large for three size classes; 12-19.9 mm CL, 20-29.9 mm CL, and 30-39.9 mm CL. These results are also presented in relation to time period, with 2001-2010 being significantly wanner than 1993-1999. Overall the results indicate that smaller juvenile American lobsters (12-19.9 mm CL) exhibit growth patterns that are significantly different from larger juveniles (20-39.9 mm CL) and that an increase in water temperature over the past 18 years has had a varied, but in some cases significant, effect on relative growth, intermolt interval, and molt probability. In order to test the indirect influence of predation on lobster behavior I used acoustic telemetry within large-scale (3-6 acre), enclosed embayments. I hypothesized that the presence of a large predator, Atlantic cod, would induce lobsters to move less and seek refuge to avoid predation. I found that the addition of cod into the embayments significantly reduced the distance lobsters traveled from their shelters, reduced home range area, and reduced the frequency of foraging outside of shelter area. Overall, the observed increase in water temperature in the past 18 years may have increased both the frequency of molting and growth, and in the aftermath of the collapse of many groundfish stocks the distance and frequency of foraging, and thus food intake and growth, may have increased in response to a release from predator-avoidance behavior. These results may explain some of the factors resulting in an exponential increase in the Gulf of Maine lobster stock over the past three decades.

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