Climate change and fish 2. North Atlantic

Question 1

Describe the change in ocean heat.

Answer 1

• Since 1955, 84% of ‘global warming’ in the ocean
• Some areas changing faster than others
• NE Atlantic and the Mediterranean perhaps experiencing among the biggest warming trends!
• Recognition that the oceans are a very important repository of heat.

Ocean conveyor belt. Waters rise in pacific and sink in the North Atlantic – hence particularly warm conditions in the North Atlantic.

*

Question 2

North Sea - one of the most studied oceans of the world.

What paper compares sea temperature to fishery catch?

Answer 2

Graph

Simpson SD et al. (2011) Current Biology 21: 1565-1570

Graph shows an increase in sea surface temperature and sea bed temperature, alongside standardized fishing mortality reflecting a decline in fishing pressure and the implementation of the common fisheries policy – EU.

Bottom temperatures (SBT) lower than sea surface temperature (SST), but both show a net increase. And while fishing pressure increased up to start of the 1990s, has been declining since.

Question 3

What notes can be made about the warming of the north sea?

Answer 3

Warming but not simple: (1) warming in summer but particularly in winter (2) v rapid warming in late 1980s (3) warming with increasing latitude in S North Sea, but N Atlantic Current waters make N North Sea waters slightly warmer

Question 4

How to fish fair in relation to temperature.

Answer 4

Different species will have a different thermal physiological thermal optimal, but they will all show the same trend of rising from a low relative thermal performance at low temperatures to a higher one (1) between 10 and 20 degrees and fall again by 30 degrees.

Question 5

What other changes are occurring in the North Sea, aside from a direct temperature change.

Answer 5

Temperature 1.6°C increase over 25 years, 1°C rise in 1988-89

Whilst there are increases in sea surface and bottom temperature, other factors are ongoing. Also a measure of the inflow of water from the northern north sea which varies over time.

• Gulf Stream position (GSI - Gulf Stream Index - how strong it is): overall northerly shift?
• N Atlantic weather (North Atlantic Overturning Circulation): overall shift to more positive NAO?
• North Sea inflow from Atlantic: weakening since 1990
• Salinity – decline since 1990, greater precipitation on the land.
• Some fishing impacts may be similar to warming effects (e.g. beam trawl intensity greater in the southern North Sea, loss of southern subpopulations more likely)(though lack of deepening in non-target species)

Question 6

What is ICES

Answer 6

International Bottom Trawl Survey data for ICES 1° X 1° North Sea boxes: 118 taxa of which six were multispecies, standard GOV trawl designed for pelagic and demersal species.

International Council for the Exploration of the Sea.

Routinely samples each year within the same box.

Question 7

What does the ICES data show from 1980 to 2005?

Answer 7

Hiddink J, ter Hofstede R (2008) Global Change Biology 14: 453-460

An increase from 60 species to 85 species in 2005.

When plotted against temperature it shows a +ve correlation and shows species moving north.

Question 8

Give an example of a southern range expansion of a warm water fish in the north sea.

Answer 8

• Trisopterus luscus - Bib
• Lusitanian (warm water - of countries like Portugal ) species
• Mean temp 17.6 °C
• Temp range 4.4 °C - prefers warmer conditions than north of UK
• Warm thermal preference, generalist
• Non-target - moving north, maybe an indirect of something to do with fishing but cannot say its a direct effect of fishing.
• Less abundant
• Less widespread

Question 9

Give an example of a southern range expansion of a cold-water fish in the north sea.

Answer 9

• Melanogrammus aeglefinus
• Boreal (cold water) species
• Mean temp 13.7 °C
• Temp range 2.4 °C
• Coldwater, thermal specialist
• Target -
• Abundant
• Widespread
• Northern movement of the southern boundary of the haddock distribution

Question 10

Trends in life history traits: size, and age and length at maturity

Nick paper

Answer 10

Perry AL et al. (2005) Science 308: 1912-1915

The shifting fish are smaller, maturing at a smaller size and maturing earlier.

Question 11

Shifts in North Sea fish species

Nick paper

Range shifts in three species

Answer 11

Perry et al 2005

We show that the distributions of both exploited and nonexploited North Sea fishes have responded markedly to recent increases in sea temperature, with nearly two-thirds of species shifting in mean latitude or depth or both over 25 years. For species with northerly or southerly range margins in the North Sea, half have shown boundary shifts with warming, and all but one shifted northward. Species with shifting distributions have faster life cycles and smaller body sizes than nonshifting species. Further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interactions.

Species shifting range in relation to temperature and time (bib, blue whiting, lesser weaver, Norway pout, scaldfish, witch) on average 2.2. km/yr

Birds, butterflies and Alpine herbs: 0.6 km/yr (also upward) -

in spite of physics of water these ranges are moving surprisingly fast

Cod target fish, snake blenny not at all.

(maybe read paper)

Question 12

International Bottom Trawl Survey data: important differences between regions

Nick Paper

Answer 12

Increasing warm-water species e.g. pipefish, red mullet and gurnard

W Scotland shows declines in species richness and temperature: no trend for Lusitanian (warm) species but a decrease in Boral (cold) species

• Overall increase in the total number of species is driven particularly by the warm water lactarian species.
• Diamonds – Lusitanian species
• Crosses – boreal species
• Conversely in the waters west of Scotland – not obvious that there is any trend in the Lusitanian species but being driven by the boreal species.
• Expanding species generally small and southerly species closer to the northern boundary
• Range decreases: large, far from northern latitude boundary

Question 13

Nick Paper

Temporal trends in North Sea Fish Size

Answer 13

Baudron AR et al. (2014) Global Change Biology 20: 1023-1031

Changes in theoretical maximum size (L∞) over time (1970-2010) in 13 ‘stocks’ of N Sea fish: 9 (c-f, h-l) show net negative trends, 4 less obvious…

L infinity – a measure of how big they would grow if they went on growing forever

13 stocks altogether, 9 negative trend over time

Maximum body size in 9 species out of thirteen, tend to decline over time.

Question 14

Issues of depth

Describe the survey looking at thermal tolerances, ecology, biogeography and the exploitation status.

Answer 14

Dulvy NK et al. (2008) J Applied Ecology 45: 1029-1039

North Sea English groundfish survey (ie. not fisheries landings) data:

• Not fisheries landing – a survey that is done annually
• Statistical rectangles which are routinely sampled, any one year around 70 are sampled using the same gear
• Look at the trend in data in relation to the animal’s thermal preference, ecology, biogeography, boreal vs Lusitanian species.
• They find latitude effects – particularly northwards shifts in distribution
• Assemblages analysed for thermal preferences, ecology, biogeography and exploitation status

Question 15

Nick paper

the survey looking at thermal tolerances, ecology, biogeography and the exploitation status.

Depth trends

Answer 15

• Whilst finding evidence of shifts in latitude effects, a change in the vertical depth distribution showed a stronger trend.
• This was significant for 11 species, with a deepening among those species of 5.5 m a decade.
• Overall species 3.6 m a decade
• Some species up to 10 m a decade.
• Bib and sole are the only statistically significant shallowing species

(Weak latitude effect: Northward shift of many abundant species

Southward shift of some warm tolerant species

Fishery exploitation important factor for some species e.g. cod)

Question 16

Nick paper

Biogeographic shifts

Answer 16

Simpson SD et al. (2011) Current Biology 21: 1565-1570

Begin by looking at shifts in the biogeographic makeup in these communities over time.

The time plots give us an idea of how the fish community changes spatially in the North Sea and out to the wider Atlantic

Biogeographic clusters based on species presence-absence data indicate relative stability over time: only 4 of the 12 clusters showed distribution change over 30 year period.

What else is going on? Found in the long term data - most species are increasing in abundance (27out of 50 significantly) (red mullet), yet some species (9 significant) (Atlantic Cod) have decreased. An explanation is that these are the species vulnerable to exploitation rather than to temperature. Exploitation effect is so strong it outweighs the effect of temperature.

Question 17

Arctic environmental changes

Answer 17

Circulation in the Barents sea has a meeting between cold and warm water masses, the cool water extanded further south in 1980 than in 2000.

The extent of the winter ice is, overall declining. The winter sea-level atmospheric pressure is showing a circular trend and the summer temperature is increasing.

Mueter FJ, Litzow MA 2008 Ecological Applications 18: 309-320

• Catch per unit effort is increasing.
• More subantarctic species are being caught
• Mean trophic position is tending to increase
• Species richness is increasing

Question 18

Nick paper: movement of species polewards, classified into three groups.

Answer 18

Fossheim M et al. 2015 Nature Climate Change 5: 673-677

Atlantic community centre (mean bottom temp 3.46˚C, dominated by cod, haddock etc) moved 141 km north, while Arctic centre (temp 1.08˚C, dominated by bigeye sculpin, Greenland halibut etc) moved 159km north

intermediate species has shifted and the number of assemblages that can be regarded as being arctic has tended to thin.

Question 19

Food web and polar cod

Answer 19

Cod very important for channelling copepod production to higher trophic levels

Polar cod a pivotal species.

Worried about competing species

Cod – atlantic cod

Question 20

Study in the Barents Sea

Polar cod vs boreal species

diet overlap?

Polar cod show a large spatial variation in their diet, but Calanus makes up a large part of their diet.

Not a huge amount of overlap between prey, so they may not be competing too much for food.

Answer 20

Cod and haddock not actually competing for the same resources

Question 21

Polar cod and ice

Answer 21

Juvenile polar cod muscle Is quite similar in carbon to the ICE POM and fairly far removed from planktonic particulate organic matter.

Sympagic primary producers – refers to the spaces within the ice.

Bulk carbon stable isotopes of the polar cod muscle closer to ice POM than planktonic POM: under the ice as nursery habitat for polar cod. What happens with ice retreat

Question 22

Polar vs boreal food webs

Answer 22

Compare food web from boreal waters from those in the arctic

233 trophospecies - cant always analyse down to species level. (8 basal species, 43 zooplankton, 79 benthic, 77 fish) and 2192 feeding links.

As things become more boreal the food webs will become less modular – and more generalist species will come in (cod, haddock and species of red fish ect).

Arctic food web: more modules, fewer generalist species. These trends reversed with ‘borealisation’ – inclusion of major boreal species including Atlantic cod, haddock and redfish

Question 23

Polar cod has low optimal temperature for growth: what will happen with warming?

Nick study

Answer 23

Kunz KL et al. 2016 Polar Biology 39: 1137-1153

Polar cod has low optimal temperature for growth: what will happen with warming?

Polar cod growth and intake increase little, while those of Atlantic cod increase with warming (possible acidification effects).

Atlantic cod does well as the temperature increases, increasing their daily food intake and growth. Polar cod show a much-reduced trend as decrease after 8 degrees.

Polar cod food conversion and condition decline relative to Atlantic cod with warming and acidification.

Condition factor is a measure of the body mass relative to the length of the animals. With an increase in temperature from 0 degrees Atlantic cod increases whilst polar cod decreases from 3 degrees.

This study investigates the competitive strength of the co-occurring gadoids under ocean acidification and warming (OAW) scenarios.

Therefore, we incubated specimens of both species in individual tanks for 4 months, under different control and projected temperatures (polar cod: 0, 3, 6, 8 °C, Atlantic cod: 3, 8, 12, 16 °C) and PCO2 conditions (390 and 1170 µatm) and monitored growth, feed consumption and standard metabolic rate.

Our results revealed distinct temperature effects on both species. While hypercapnia by itself had no effect, combined drivers caused nonsignificant trends.

The feed conversion efficiency of normocapnic polar cod was highest at 0 °C, while optimum growth performance was attained at 6 °C; the long-term upper thermal tolerance limit was reached at 8 °C.

OAW caused only slight impairments in growth performance. Under normocapnic conditions, Atlantic cod consumed progressively increasing amounts of feed than individuals under hypercapnia despite maintaining similar growth rates during warming.

The low feed conversion efficiency at 3 °C may relate to the lower thermal limit of Atlantic cod. In conclusion, Atlantic cod displayed increased performance in the warming Arctic such that the competitive strength of polar cod is expected to decrease under future OAW conditions.

Question 24

Overview

Answer 24

Overview

Fish species richness increase in 2/3 North Sea regions

Fish shifting to deeper water, most becoming more abundant, with implications for fisheries

Some changes attributable to warming, but other factors help explain the trends (e.g. changes in salinity and fishing pressure)

‘Borealisation’ of Arctic is bringing new species and less modular (more connected) food webs

Polar cod illustrates the plight of some species as warming progresses: loss of habitat, potential competition with climate migrants, impacts on basic physiology, it can’t move northward forever (especially as Arctic Ocean deep basin)

Dramatic ways in which we are finding significant changes happening that are attributed to temperature effect alongside other factors.

Question 25

What ways is climate change impacting on fish stocks?

Answer 25

• Species richness
• Body Size
• Abundance
• Horizontal/ geographic distribution
• Depth distribution
  *

Question 26

Northwards Shifting Marine Fish Species, the Wrasse.

Method.

Answer 26

Climate Change and Genetic Structure of Leading Edge and Rear End Populations in a Northwards Shifting Marine Fish Species, the Corkwing Wrasse (Symphodus melops) – Knutsen et al., 2013

Corkwing wrasse (Symphodus melops)

Method:

• corkwing wrasse is presently distributed along the European coasts, from southern Portugal to western Norway except along the sandy coast between the Netherlands and Denmark – Was present in the Mediterranean but not almost extinct due to warming
• Study sites from Algarve to Scandinavia
• Samples caught by fish pots in UK, Seining in Norway +Sweden and spearfishing in Spain and Portugal
• DNA was extracted

Question 27

Northwards Shifting Marine Fish Species, the Wrasse.

Results

Answer 27

The current increase in the species abundance in Scandinavia is not a result of immigration from south, which would have rapidly wiped out genetic differences, but by increased growth of local populations, most likely because rising sea temperatures in this northern range are favourable to the species’ requirements. While the corkwing wrasse may find suitable rocky shores to continue its shift further north as water temperatures continue to rise in the coming decades, they bring with them only a part of the species’ original genetic variability and the loss could impair its long-term survival in a changing environment.

Results:

• Markedly increase in abundances in Scandinavia compared to 1980 levels when the temperature started to increase – potentially still undergoing northward shift
• The genetic difference between Scandinavian populations and southern populations – Maybe due to lack of suitable habitat over some distance may have prevented population connectivity – Netherlands and Denmark have sandy areas – this species preference is for rocky substrate – less genetic variability in Scandinavian
• Differences could be due to historical range shifts - Most likely made possible by the presence of suitable shorelines along Doggerland that temporally acted as a migration path from UK to the Skagerrak shores. Following the subsequent submergence of Doggerland the species was apparently deprived of this northward path, and migration to Skagerrak ceased.

Question 28

Continental Shelf-Wide Response of a Fish Assemblage to Rapid Warming of the Sea

background/method

Answer 28

Continental Shelf-Wide Response of a Fish Assemblage to Rapid Warming of the Sea – Simpson et al., 2011

We assessed the full impacts of warming on the commercially important European continental shelf fish assemblage using a data-driven Eulerian (grid-based) approach that accommodates spatial heterogeneity in ecological and environmental conditions.

We analyzed local associations of species abundance and community diversity with climatic variables, assessing trends in 172 cells from records of >100 million individuals sampled over 1.2 million km(2) from 1980-2008.

We demonstrate responses to warming in 72% of common species, with three times more species increasing in abundance than declining, and find these trends reflected in international commercial landings
Background/method:

• To investigate the effects of temperature variability on abundance of demersal species on the European continental shelf
• 3 decades of high-resolution fisheries-independent data - analysis encompassed approx. 1.2 million km2 of seabed and depths ranging from 5-592 m

Question 29

Continental Shelf-Wide Response of a Fish Assemblage to Rapid Warming of the Sea

Results

Answer 29

Results: – Simpson et al., 2011

• Between 1982 – 2006 North Sea increased in mean temperature by 1.31 degrees Celsius
• Majority of species increased in response to warming – Ones that decrease were often commercially targeted – interaction that fishing applies increased pressure
• Saying that temperature alone will not predict the effects of climate change
• Studies exploring shifts in central latitudes may miss important spatial variability and local response. E.g. poleward shift in abundances as would be expected under climate envelope scenarios was only observed in 13/36 species – despite significant and ubiquitous changes in temperature
• Analysing local changes in abundance without assuming a range shift during warming and allowing for uneven distribution, linked to unsuitable habitats – Identified changes in abundance in the North Sea in 39/50 most common species –
• Impact of these abundant changes on fisheries – species such as haddock and cod fell by half during period of study, but the 27 species identified during warming conditions increased 2.5 times