UPWELLING AND IT'S EFFECT ON FISHERIES

How up-welling in ocean effects fisheries is described here.

1. WEST BENGAL UNIVERSITY OF ANIMAL & FISHERY SCIENCES FACULTY OF FISHERY SCIENCES FRM – 329 A SEMINAR ON UPWELLING AND FISHERIES PRESENTED BY: SOURAV BHADRA B.F.Sc 3 rd yr. 2 nd sem. ROLL NO. F/2016/29 PRESENTED TO: Prof. t.s.Nagesh Course teacher DEPT. OF FRM

2. INTRODUCTION: What is upwelling? Upwelling is an oceanographic phenomenon that involves wind -driven motion of dense, cooler, and usually nutrient -rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water . The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton . Due to the biomass of phytoplankton and presence of cool water in these regions, upwelling zones can be identified by cool sea surface temperatures (SST) and high concentrations of C hlorophyll-a In turn this two factors helps fishermen to identify the PFZ(Potential Fishing Zone)

3. Mechanisms: The three main drivers that work together to cause upwelling are wind , Coriolis effect , and Ekman transport . They operate differently for different types of upwelling, but the general effects are the same. In the overall process of upwelling, winds blow across the sea surface at a particular direction, which causes a wind-water interaction. As a result,the water is transported a net of 90 degrees from the direction of the wind due to Coriolis forces and Ekman transport.

4. Ekman transport causes the surface layer of water to move at about a 45 degree angle from the direction of the wind, and the friction between that layer and the layer beneath it causes the successive layers to move in the same direction. This results in a spiral of water movement down the water column. Then, it is the Coriolis forces that dictate which way the water will move; in the Northern hemisphere, the water is transported to the right of the direction of the wind. In the Southern Hemisphere, the water is transported to the left of the wind.

5. TYPES OF UPWELLING: There are five types of upwelling: Coastal upwelling, Large-scale wind-driven upwelling in the ocean interior, Upwelling associated with eddies, Topographically-associated upwelling, and Broad-diffusive upwelling in the ocean interior.

6. Coastal Upwelling: Coastal upwelling is the best known type of upwelling, and the most closely related to human activities as it supports some of the most productive fisheries in the world. This upwelling process occurs at a rate of about 5–10 meters per day, but the rate and proximity of upwelling to the coast can be changed due to the strength and distance of the wind. Coastal upwelling exists year-round in some regions, known as major coastal upwelling systems, and only in certain months of the year in other regions, known as seasonal coastal upwelling systems. Many of these upwelling systems are associated with a relatively high carbon productivity and hence are classified as Large Marine Ecosystems

7. Contd …… Worldwide, there are five major coastal currents associated with upwelling areas: the Canary Current (off Northwest Africa ), the Benguela Current (off southern Africa ), the California Current (off California and Oregon ), the Humboldt Current (off Peru and Chile ), and the Somali Current (off Somalia and Oman ). All of these currents support major fisheries. The four major eastern boundary currents in which coastal upwelling primarily occurs are the Canary Current, Benguela Current, California Current, and Humboldt Current. The Humboldt Current or the Peru Current flows west along the coast of South America from Peru to Chile and extends up to 1,000 kilometers offshore.These four eastern boundary currents comprise the majority of coastal upwelling zones in the oceans.

8. Variations: Upwelling intensity depends on wind strength and seasonal variability, as well as the vertical structure of the water , variations in the bottom bathymetry , and instabilities in the currents . In temperate latitudes , the temperature contrast is greatly seasonably variable, creating periods of strong upwelling in the spring and summer, to weak or no upwelling in the winter. For example, off the coast of Oregon, there are four or five strong upwelling events separated by periods of little to no upwelling during the six-month season of upwelling. In contrast, tropical latitudes have a more constant temperature contrast, creating constant upwelling throughout the year. The Peruvian upwelling, for instance, occurs throughout most of the year, resulting in one of the world's largest marine fisheries for sardines and anchovies .

9. Effects of Upwelling on Fishery Biodiversity and productivity: Since upwelling regions are important sources of marine productivity, and they attract hundreds of species throughout the trophic levels, the diversity of these systems has been a focal point for marine research . While studying the trophic levels and patterns typical of upwelling regions, researchers have discovered that upwelling systems exhibit a wasp-waist richness pattern. In this type of pattern, the high and low trophic levels are well-represented by high species diversity. However, the intermediate trophic level is only represented by one or two species. This intermediate trophic layer, which consists of small, pelagic fish usually makes up about only three to four percent of the species diversity of all fish species present. The lower trophic layers are very well-represented with about 500 species of copepods , 2500 species of gastropods , and 2500 species of crustaceans on average. At the apex and near-apex trophic levels, there are usually about 100 species of marine mammals and about 50 species of marine birds.

10. Contd …… The vital intermediate trophic species however are small pelagic fish that usually feed on phytoplankton . In most upwelling systems, these species are either anchovies or sardines, and usually only one is present, although two or three species may be present occasionally. These fish are an important food source for predators, such as large pelagic fish, marine mammals, and marine birds. Although they are not at the base of the trophic pyramid, they are the vital species that connect the entire marine ecosystem and keep the productivity of upwelling zones so high.The food chain follows the course of: Phytoplankton → Zooplankton → Predatory zooplankton → Filter feeders → Predatory fish → Marine birds, marine mammals

11. Animal movement: The second major consequence of upwelling involves its effect on animal movement. Upwelling affects the movement of animal life in the area. Tiny larvae—the developing forms of many fish and invertebrates—can drift around in ocean currents for long periods of time. A strong upwelling event can wash the larvae far offshore, endangering their survival. Therefore, upwelling can be a mixed blessing to coastal ecosystems. It can infuse coastal waters with critical nutrients that fuel dramatic productivity, but it can also rob coastal ecosystems of offspring required to replenish coastal populations.

12. Fisheries in upwelling regions — with special reference to peruvian waters: A 25,900-square-kilometer (10,000-square-mile) region off the west coast of Peru,undergoes continual coastal upwelling and is among the richest fishing grounds in the world. The anchovy population that is the basis of the Peru fishery,is a phytoplankton feeding species, supported by an upwelling based ecosystem. The fish is very short-lived and grows rapidly — both criteria for high turnover rate — high yield fisheries. The maximum sustainable yield(MSY) is around 10 million metric tons.

13. Contd ….. Upwelling generates some of the world’s most fertile ecosystems. Overall, coastal upwelling regions only cover 1 percent of the total area of the world’s oceans, but they provide about 50 percent of the fish harvest brought back to shore by the world’s fisheries.

14. Conclusion: Deep ocean water is more nutrient-rich than surface water simply because things (nutrients, plankton carcasses, fish carcasses) in the ocean sink. Upwelling brings those lost/sunk nutrients back to the surface, which creates "blooms" of algae and zooplankton, which feed on those nutrients. These blooms then become feeding grounds for plankton feeders, then fish, etc , sustaining ocean life that lives near the surface.

15. Reference: https://www.nationalgeographic.org/encyclopedia/upwelling https://en.wikipedia.org/wiki/Upwelling https://oceanexplorer.noaa.gov/facts/upwelling.html https://www.quora.com/Why-is-upwelling-important-to-marine-life https://www.nwfsc.noaa.gov/research/divisions/fe/estuarine/oeip/db-coastal-upwelling-index.cfm Sarhan T, Lafuente JG, Vargas M, Vargas JM, Plaza F. (1999). Upwelling mechanisms in the northwestern Alboran Sea. Journal of Marine Systems Lalli , C.M., Parsons, T.R. (1997) "Biological Oceanography: An Introduction" Oxford: Elsevier Publications .

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