Date of Award

1-2013

Rights

© 2013 Erin Wilkinson

Document Type

Thesis

Degree Name

Master of Science in Marine Sciences

Department

Marine Science

First Advisor

Phil Yund

Second Advisor

Jonathan Grabowski

Third Advisor

Kathryn Ono

Fourth Advisor

Graham Sherwood

Abstract

The American lobster, Homarus americanus, is an important consumer in the Gulf of Maine benthic community and supports the most valuable fishery in New England. Many fish predators that feed on juvenile lobster are found in the Gulf of Maine, but their abundance has varied over the previous decades. For example, striped bass, Morone saxatilis, have recovered from near extinction to become a viable recreational fishery on the east coast, and previous work examining the gut contents of striped bass found that juvenile lobsters were a large component of their diet during the summer in Massachusetts. However, striped bass diet has not been examined extensively in the Gulf of Maine and this raises questions as to how important lobster may be to striped bass diet in southern Maine coastal waters. There are also many management strategies in place to help restore other fish species known to consume juvenile lobster, such as Atlantic cod, to the Gulf of Maine. It has been suggested that the abundance of lobster may be inversely related to the abundance of coastal groundfish in the Gulf of Maine. In addition to consumptive effects through feeding activity these predators may also have non-consumptive effects on their targeted prey species by causing lobster to alter their behaviors. It is unclear what consumptive and non-consumptive effects the return of these large fish predators may be having on juvenile lobster in the Gulf of Maine.

Chapter 1 examines the food habits of striped bass in Southern Maine coastal waters, with an emphasis on how important lobster is to their diet. Using stomach contents and stable isotope analysis I found that for all sizes of striped bass small pelagic fish species made of the majority of diet, and for large and extra-large fish crustaceans (lobster) were found more often than in the stomachs of smaller fish. Stable isotope analysis revealed that larger striped bass expressed stronger benthic signals of δ13C, indicating that prey such as lobsters are more important to larger striped bass diet in Southern Maine than stomach contents revealed.

The 2nd chapter presented here examines what sizes of juvenile lobsters are most susceptible to predation, and how juvenile lobster anti-predator response varies among different predators (striped bass, cod, and sea raven). I found that small lobsters (<45mm carapace length) are most susceptible to predation, and observed that the strength of anti-predator responses displayed by lobster varied with predator type. Lobsters reacted to the presence of Atlantic cod or sea raven by decreasing activity levels and increasing shelter use, but did not alter behavior in the presence of striped bass. This varying level of response seems consistent with differences in predator foraging modality.

Taken together, the results of these two studies can be used to increase our understanding of what long term consumptive and non-consumptive effects can be expected for juvenile lobsters in southern Maine if we continue to see the return of large fish to this region.

Comments

Master's thesis

This digital object has been funded in part with Federal funds from the National Science Foundation, Division of Graduate Education, under Award No. #0841361, "The Interactions of Biology, Chemistry and Physics at the Land-Ocean Interface: A Systemic PARTnership Aimed at Connecting University and School (SPARTACUS)", to the University of New England.

Portions of this thesis were the basis for the following publication:
Wilkinson, E. B., J. H. Grabowski, G. D. Sherwood, P. O. Yund. 2015. Influence of predator identity on the strength of predator avoidance responses in lobsters. Journal of Experimental Marine Biology and Ecology 465: 107-112. Doi: 10.1016/j.jembe.2015.01.002

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