The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine

Abstract

Ocean warming can drive poleward shifts of commercially important species with potentially significant economic impacts. Nowhere are those impacts greater than in the Gulf of Maine where North America's most valuable marine species, the American lobster (Homarus americanus Milne Edwards), has thrived for decades. However, there are growing concerns that regional maritime economies will suffer as monitored shallow water young‐of‐year lobsters decline and landings shift to the northeast. We examine how the interplay of ocean warming, tidal mixing, and larval behavior results in a brighter side of climate change. Since the 1980s lobster stocks have increased fivefold. We suggest that this increase resulted from a complex interplay between lobster larvae settlement behavior, climate change, and local oceanographic conditions. Specifically, postlarval sounding behavior is confined to a thermal envelope above 12°C and below 20°C. Summer thermally stratified surface waters in southwestern regions have historically been well within the settlement thermal envelope. Although surface layers are warming fastest in this region, the steep depth‐wise temperature gradient caused thermally suitable areas for larval settlement to expand only modestly. This contrasts with the northeast where strong tidal mixing prevents thermal stratification and recent ocean warming has made an expansive area of seabed more favorable for larval settlement. Recent declines in lobster settlement densities observed at shallow monitoring sites correlate with the expanded area of thermally suitable habitat associated with warmer summers. This leads us to hypothesize that the expanded area of suitable habitat may help explain strong lobster population increases in this region over the last decade and offset potential future declines. It also suggests that the fate of fisheries in a changing climate requires understanding local interaction between life stage‐specific biological thresholds and finer scale oceanographic processes.

Projecting ocean acidification impacts for the Gulf of Maine to 2050

“…Experiments on spatial and seasonal impacts on marine organisms at multiple life stages are limited and require the synergy of chemical and physical oceanography with biological responses. Nearshore regions are common nursery grounds for both vertebrate and invertebrate marine species (Stevenson et al, 2014;Goode et al, 2019) but are poorly represented in our models. Subsequent projections for such critical habitats and inclusions of new studies on key regional economic species, including the understudied Jonah crab and goosefish, are needed to fully assess vulnerabilities and promote adaptive management plans.…”

The cresting wave: larval settlement and ocean temperatures predict change in the American lobster harvest

“…For example, if over the years settlement has spread to greater depths, beyond the current survey, the index could overstate predicted recruitment declines (Goode et al. ). Information on deep water settlement remains limited.…”

“…A bias in the ALSI index could arise if the areal coverage of YoY recruitment has changed over time. For example, if over the years settlement has spread to greater depths, beyond the current survey, the index could overstate predicted recruitment declines (Goode et al 2019 Broadly, all predictive models relying on life history information and ecological parameters are subject to sampling bias and process error, which can impair accurate predictions (Patterson 2001). Process error can arise from uncertainty in biological parameters (Newman et al 2006); in our case natural mortality and growth function.…”

Dynamic changes in American lobster suitable habitat distribution on the Northeast U.S. Shelf linked to oceanographic conditions

“…The change in temperature is associated with changes in American lobster population size and distribution, with both centers of lobster biomass and fisheries landings shifting northeast since the 1970s (Pinsky & Fogarty, 2012). Projections of increasing temperatures over the next century (Saba et al., 2016) suggest that temperature will continue to have an impact on critical American lobster life history traits and the anticipated distribution of thermal habitat for lobster (Fogarty et al., 2007; Chang et al., 2010; Tanaka & Chen, 2015; Tanaka & Chen, 2016; Georgas et al, 2016; Rheuban, Kavanaugh, & Doney, 2017; Goode, Brady, Steneck, & Wahle, 2019). Warming water conditions may have a disproportionate effect on lobster at the southern end of their latitudinal range due to impacts on their life history.…”