Ecology and Vulnerability

Bluefin Tuna

Many studies provide strong evidence that marine fish and elasmobranch species respond to climate change through geographical range (Nye et al., 2009) and phenology shifts (Staudinger et al., 2019; Langan et al., 2021). Studies of range shifts generally use long-term federal datasets from spring and fall bottom trawl (NOAA Fisheries, 2022) and ichthyoplankton Ecosystem Monitoring (EcoMon) (Walsh et al., 2015) surveys of the continental shelf or by state and private surveys of regional bays and estuaries (Morson et al., 2019, Snyder et al., 2019; Langan et al., 2021). These extensive monitoring programs have shown that centers of population biomass for most marine fish species are shifting poleward towards higher latitudes and to greater depths at rates that exceed terrestrial species (Lenoir et al., 2020). These general trends are projected to continue under future climate scenarios of modeled habitat abundance (Kleisner et al., 2017), suitable thermal habitat (Morley et al., 2018), and relative population biomass (Allyn et al., 2020).


An analysis of 42 species of marine fish and invertebrates (RSGCN and non-RSGCN species) found in continental shelf waters of the Northeast region between 1974 and 2022, showed the community has shifted on average 0.75 degrees (83.83 km) north during spring, and 0.61 degrees (68.27 km) north during fall. The community also experienced a change in average depth of 22.4 meters and 8.6 meters deeper in spring and fall, respectively (NOAA Fisheries, 2022). Similar to patterns observed at the community scale and for non-RSGCN species, the direction, rate, and magnitude of range shifts varies widely among RSGCN marine fishes and elasmobranchs sampled during this period; responses in range changes span -0.51 km southward in Winter Skate, to 2.25 km northward in Black Sea Bass during spring, and -0.21 km northward in Atlantic Herring to 2.05 km northward in Black Sea Bass during fall. Depth range shifts spanned from -61.08 meters deeper in Atlantic Herring to 12.41 km shallower in Atlantic Cod in spring and -50.88 meters deeper in Atlantic Herring to 31.20 meters shallower in Atlantic Halibut during fall (NOAA Fisheries, 2022).


Shifts in phenology are more difficult to track compared to range shifts in aquatic species because observations need repeated observations within a narrow and set area over multiple decades (Staudinger et al., 2019). Several multi-species analyses have shown phenological shifts in the occurrence of larval phases of demersal groundfishes (Walsh et al., 2015), growth and productivity of population biomass (Henderson et al., 2017), as well as seasonal migration patterns (both ingress and egress) and residence times in estuaries systems such as Narragansett Bay, Rhode Island (Langan et al., 2021).

As species make distributional changes in range and phenology, primarily in response to warming sea surface and bottom temperatures, entire assemblages of marine species are reshuffling and reorganizing across Northeast coastal ecosystems (Weiskopf et al., 2020; Staudinger et al., 2021). Examples of changes in community structure through altered species diversity, population size, and density have been documented across the Northeast continental shelf (Friedland et al., 2020) and in estuaries including Little Egg Inlet, New Jersey (Morson et al., 2019), Narragansett Bay, Rhode Island (Langan et al., 2021), and Long Island Sound off of New York and Connecticut (Snyder et al., 2019). Ensembles of warm-water-associated species that are moving north into temperate habitats are generally replacing cold-water-associated species, which are moving to deeper depths and higher latitudes in search of cold-water refugia (Friedland et al., 2020; Pershing et al., 2021). 

On a global scale, warming has led to a decrease in body size (Sheridan and Bickford 2011) but this varies widely by species and local conditions. The indirect effects of morphological and behavioral changes combined with shifting distributions are changing predator-prey and competitive relationships among associated marine fish species and resulting in novel trophic interactions (Staudinger et al., 2021). Most models that project range shifts currently do not account for species interactions (Pearson and Dawson, 2003; MacPherson et al., 2021); this is an area of active research as changes in trophic relationships are hypothesized to be more important for species survival under future conditions than environmental conditions (Louthan et al., 2015, Staniczenko et al., 2017). In addition, the combined stress from warming ocean temperatures, decreased dissolved oxygen, and ocean acidification is increasing the prevalence and vulnerability to disease and predation.

Shifts in Ranges, Elevation, or Depth

Bluefin Tuna were collected off the coast of Greenland for the first time in 2012 due to warming sea temperatures and the abundance of one of their main prey species (Mackenzie et al., 2014), the Atlantic Mackerel (Scomber scombrus), which has recently expanded its range north as well (Astthorsson et al., 2012). From 1993 to 2020, warming sea surface temperature has led to Bluefin Tuna in the Atlantic increasing the total area of their range by 96 km2 per year and shifting their biomass center an average of 2 km per year north and 3 km per year east (Hansell et al., 2022). Models incorporating climate projections based on the highest emissions scenario (RCP 8.5) suggest this trend will continue, with Bluefin Tuna shifting their northern range limit 6.38 decimal degrees in the western Atlantic by 2099, though their abundance is expected to decrease throughout their range (Erauskin-Extramiana et al., 2022). 

Shifts in Phenology

Bluefin Tuna mostly spawn in the Gulf of Mexico and have a short spawning window due to rising temperatures in May and June; however, by 2090, warming seas may shift their spawning window to March and April but may severely limit the available habitat (Muhling et al., 2014). While spawning habitat will likely decrease and metabolic stress may increase in the sub-tropics, the Bluefin Tuna may be able to take advantage of a more suitable habitat further north (Muhling et al., 2016).

Changes to Morphology or Physiology

Bluefin Tuna larvae experimentally exposed to varying degrees of salinity and pH, conditions that may occur in the future due to climate change, had lower rates of survival in extreme highs and lows in salinity but had similar survival rates in different levels of pH (RuizJarabo et al., 2022).