Ecology and Vulnerability

Atlantic Herring

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 Range, Elevation, or Depth

Between the periods of 1974-1977 to 2019-2022, juvenile and adult Atlantic Herring shifted their spring range across the Northeast continental shelf region by 1.24 degrees (138.7 km) northwards, and their range has contracted by 0.01 degrees (2.16 km). Conversely, during fall, their range shifted 0.21 degrees (23.43 km) south and expanded by 0.91 degrees (101.07 km) between 1974-1976 to 2019-2022. Atlantic Herring have shifted to deeper waters during spring and fall by 61 meters and 50.8 meters between 1974-1977 to 2019-2022 and 1974-1976 to 2019-2022, respectively (NOAA Fisheries, 2022). Larval Atlantic Herring shifted their distribution further offshore between the periods of 1977-1987 and 1999-2008 in the Georges Bank to Gulf of Maine regions (Walsh et al., 2015). Over the same periods, adult and larval life phases of Atlantic Herring exhibited synchronous distributional shifts to offshore waters during spring across the Northeast continental shelf region (Walsh et al., 2015). Atlantic Herring are projected to experience a significant loss of relative biomass during spring and fall by 2050 across the Northeast continental shelf with larger declines in the Southern New England – Mid-Atlantic compared to the Gulf of Maine under mean model projections using the RCP 8.5 scenario (Allyn et al., 2020). There is low certainty that Atlantic Herring will shift the centroid of their range across the Northeast continental shelf by 94.3 km under RCP 2.6 and 380.0 km under RCP 8.5 by the end of the century (2081-2100), with projected changes of available thermal habitat of 1.7% under RCP 2.6 and -12.6% under RCP 8.5 when compared to the period of 2006-2020 (Morely et al., 2018). In places where Atlantic Herring lay their eggs deep in the water column, which typically have low concentrations of oxygen but high levels of CO2, their spawning habitats will be especially at risk of increasing water temperatures and ocean acidification brought on by climate change (Leo et al., 2018). Eggs incubated in experimental conditions set to match future projections of temperature and CO2 demonstrated more malformations and smaller-sized larvae at hatching than those incubated in conditions more similar to the current temperature and CO2 levels (Leo et al., 2018). Similarly, experimental evidence suggests that future levels of anticipated ocean acidification will cause organ damage, smaller size, stunted development, and poor condition of Atlantic Herring larvae, with negative impacts on larvae increasing in association with higher CO2 levels (Frommel et al., 2014). Under poor growth conditions, smaller larvae will likely remain vulnerable to predation longer, affecting recruitment rates to older life phases (Frommel et al., 2014). There is still high uncertainty about how Atlantic Herring will be affected by different levels of CO2. One study found that swimming speed and foraging behavior in Atlantic Herring larvae were not affected when exposed to high levels of dissolved CO2 (Maneja et al., 2014). However, another experiment found higher temperatures alone drove slower growth rates, while increased CO2 had a negligible effect on size and survivorship, and food availability also played a large role (Sswat et al., 2018a). Similarly, larval swimming speed and searching behavior decreased under conditions of warmer temperatures and reduced food availability compared to similar temperatures but higher food availability (Allan et al., 2022). Community-level experiments suggest that Atlantic Herring larvae may benefit indirectly from increased CO2, due to increases in primary production of their primary prey - plankton, which increased larvae survival by ~19% (Sswat et al., 2018b). These studies suggest a complicated relationship between increasing ocean acidification and the survivorship of Atlantic Herring larvae, where there will likely be trade-offs between negative and positive effects.

Changes to Morphology or Physiology

Atlantic Herring contracted their winter residence time in Narragansett Bay, Rhode Island by 16 days between 1959 and 2016; however, the change was not statistically significant and could not be definitely attributed to water temperatures, possibly due to insufficient sampling (Langan et al., 2021). In the Baltic Sea, Atlantic Herring started developing from smaller (<10 mm) to larger (>15 mm) larvae 7.7 days per decade earlier between 1974 and 1996, coinciding with warming temperatures (Weigel et al., 2021).