Maine Green Sea Urchin Fishery: Scale Mismatches, Trophic Connectivity and Resilience

The Maine green sea urchin fishery is a classic boom and bust fishery. Landings peaked in 1993, and were subsequently followed by a persistent decline in urchin stocks along the coast. This document examines the fine scale dynamics relevant in the Maine sea urchin fishery. Chapter 1 describes the Maine sea urchin fishery as a coupled human and natural system. Through semi-structured interviews with harvesters, managers, and scientists, I identified mismatches between the scales at which regulations were implemented and the scales at which harvesters interact with the natural system. These mismatches potentially led to the erosion of local sea urchin populations, reducing the overall resilience of the population and precipitating the coast-wide decline in sea urchin stocks. Understanding the components of and interactions between coupled human and natural system may lead to more carefully crafted regulations that adequately reduce fishing effort to protect the biological dynamics of the green sea urchin. Chapter 2 explores harvesters’ perspective on the regional difference in the Maine urchin fishery. Conventional wisdom holds that the urchin fishery was depleted first and most completely in western Maine, which resulted in fishing effort shifting to the east. However, in the east, sea urchin landings and biomass estimates, while at low levels, appear to remain relatively stable. Through the semi-structured interviews, a harvester- derived deepwater refuge hypothesis emerged suggesting that sea urchin dynamics are different in eastern Maine as compared to western Maine. To test this hypothesis, I sought 1) to determine if sea urchins live at depths greater than 20 m and if a regional difference in depth distribution exists along the coast; and 2) to determine if sea urchins at depth may move into shallow zones. For the latter, I measured rates and distances individuals moved in the field and in pools with flowing seawater. My analysis of Maine Department of Marine Resources drop camera surveys conducted from 2001 - 2004 between 18-50 m depth revealed distinctly deeper urchin populations in eastern Maine only. Remotely Operated Vehicle (ROV) transects were conducted in eastern and western Maine to quantify algal detritus at depths greater than 20 m to identify potential food sources for deepwater urchin populations. My results suggest that there are deepwater sea urchin populations unique to eastern Maine and algal detritus abundance and biomass increase slightly towards the east. These patterns are consistent with higher summer productivity in kelp and other algae resulting from the tidally mixed and nutrient rich Eastern Maine Coastal Current. Strong ocean currents in this region likely contribute to greater delivery distances of algal detritus from rocky headlands to the deepwater pockets where sea urchins have been observed. If the rate and amount of algal detritus delivery to depth is greater in eastern Maine, the deepwater populations of sea urchins in that region would be less likely move to shallow zones due to the presence of a food source at depth. The delivery of algal detritus to depth extends the suitable habitat at which sea urchins can persist in eastern Maine possibly supporting a larger regional population of sea urchins in that region. A larger population of sea urchins could potentially be fished down a slower rate resulting in the apparent regional difference in the Maine sea urchin fishery