The productivity of fisheries plays a significant factor in human society because of influences on food supply, employment, and income. The effect of climate change on marine communities is of particular importance because of the strong influences that these communities have on marine food web function and fisheries yield. Climate can effect the function, distribution, and structure of fish communities. The distributions of fish species is expected to shift towards the poles as a result of climate change. Many studies have focused on how climate has affected abundance levels as well as the consequences of this decline. The changes in productivity of specific and whole populations will determine how these fisheries are responding to climate change. Jennings and Brander 2010 proposed that it is possible to make predictions about the community level responses to climate that are independent from knowledge about identity and dynamic of component populations. Community level approaches could be used to determine total fishery productivity, however population specific productivity will need to be based on each individual population. The fluctuation of a species population size can have negative effects in all countries. –Lauren Lambert
Jennings, Simon, and Keith Brander. “Predicting the Effects of Climate Change on Marine Communities and the Consequences for Fisheries.” Journal of Marine Systems 79.3-4 (2010): 418-26.
Jennings and Brander 2010 addresses several methods in which population and community based abundance levels change as a result of climate change. Abundance is related to total production size, so lower intercepts of size spectra in areas with low primary production means that production is reduced by a constant fraction throughout the food web. Primary production is correlated with fish production at large scales. Slopes of size spectra depend on the relative body sizes of predators and prey and efficiency of energy transfer from prey to predators. The former is measured as the mean predatory-prey mass ratio (PPMR), while the latter is mean trophic transfer efficiency (TE). Because slopes of size-spectra are constrained by these factors, the mean trophic level of the community is also constrained. Based on evidence for a relatively constant slope at a range of temperatures, it can be concluded that temperature will influence rates but will not change relative abundance at size. Jennings and Brander 2010 noted that species with faster life histories responded more rapidly to climate change. Studies also showed that smaller prey species moved while their predators did not. This could potentially disrupt the food chain if other species do not replace their absence. The effects of climate change on primary production will be the main factor driving changes in abundance and production.
Due evidence from previous publications, Jennings and Brander 2010 presented information regarding six different climate model simulations to show the response of primary production in ocean ecosystems in relation to climate change from the beginning of the industrial revolution to 2050. This provides insight to a rule-based categorization of global marine system into biogeographic production zones, estimates of change in primary production within these zones, and an overview of the limitations of making projections of ocean production. It has been suggested that global primary production may increase by 10% by 2050, however there is not much confidence in the accuracy of this estimate. Large scale plankton sampling shows actual observations of declining phytoplankton and chlorophyll levels over the past 20–50 years. This evidence is consistent with the expected consequences of reduced nutrient supply.
Over the next 4–5 decades, global marine primary production is not expected to significantly change, but there is a stronger basis for predicting changes at a regional scale particularly in the North Pacific and North Atlantic. These changes largely rely on regime scale and event scale factors such as El Niño effects. In the Arctic Ocean, a rising climate will lead to reduction in ice cover, resulting in a greater amount of phytoplankton production in these areas because of the increased availability of sunlight. While the productive area will rise, the existing food web will be disrupted. For example observations show that there has been a switch from krill to salps as the major nektonic species in some areas of the Antarctic. Increase in vertical stratification will also be a result of increased freshwater input from rivers. This is likely to result in negative consequences for fisheries and cause shifts in relative productivity of benthic and pelagic species in this size spectrum.
To assess the effects of climate change on fish communities, two methods have been proposed. Scaling up from predictions of climate on the individual species within the community could be used, or identification of aggregate properties of communities and the expected responses. Both of these approaches done simultaneously will provide the best understanding of ecological as well as community effects of climate change. Productivity of communities is likely to be predictable but species composition is not. The expected capacity to develop shipping vessel designs that allow for switching between different species will change the market in that they will need to accept and sell a more diverse range of fish and fish product. For the future, the main challenges in predicting the effects of climate change are to refine the current models for primary production at global scales as well as developing individual population based models that are consistent with community based models. Flexible ways of incorporating species dynamics in size-based models also needs to be developed.