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18 Food From the Sea Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001.

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Presentation on theme: "18 Food From the Sea Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001."— Presentation transcript:

1 18 Food From the Sea Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001

2 Fisheries Relatively primitive form of food acquisition - hunting and gathering Fishery is a renewable resource - resource exploitation at certain levels need not deplete the resource Crucial objective is to develop an appropriate management program to avoid overexploitation

3 Stock - a key concept A stock is a geographically definable population of a species that changes abundance in response to factors, relatively independently of other stocks

4 Stock - a key concept 2 Managers wish to identify stocks to manage and regulate crucial factors, such as controls on food eaten by the stock, crucial nursery grounds, sharing of stocks between political entities, such as different states or countries

5 Identification of Stocks Tags - devices inserted into fish so that they can be located subsequently and the location can be related to the site of tagging Biochemical and molecular markers - used to distinguish between stocks. If individual populations have unique markers, they are separated evolutionarily from other stocks

6 Gulf Coast bands Atlantic bands Mitochondrial DNA markers used to identify stocks of Striped Bass, Morone saxatilis

7 Crucial Life History Information Needed Range of temperatures and salinities for maximum growth Location of spawning/nursery habitat Location of feeding areas Biological information that minimizes unintended mortality during fishing

8 Stock Size Landings from fisheries are the main means of estimating stocks, although scientific sampling is also done

9 Stock Size 2 Landings can be related to stock size (= local population size) if relation to fishing effort can be determined

10 Stock Size 3 Fishing effort is a function of (1) number of boats; (2) number of individuals fishing; (3) hours spend fishing; (4) efficiency of fishing gear

11 Stock Size 4 Stock estimates take into account the catch per unit effort

12 Landings of the blue whale, as compared with effort Year Catch per catcher-day’s work

13 Fisheries Model To understand the behavior of a fishery, we have to construct a model of population change We must have an idea of the life history, which includes the mode of reproduction, the number of young produced, the survivorship, growth periodicity (seasonal) and rate of growth)

14 Nursery areaReproduction Recruitment Mortality To produce a good fisheries model, we must account for all contributions to reproduction, growth, and mortality, throughout the life cycle of the fishery resource species.

15 Frequency Carapace length (mm) Age classes of the lobster Panuliris ornatus. Curved line estimates age classes from the more discontinuous distributin of the histogram. Note the older age classes to the right, which are more indistinct. Identification of Age Classes by Size:

16 Model of Fishery Population In words, this means that the change of mass (  W) from Year t-1(previous year) to year t (the current year) equals the growth  W - the loss of mass in mortality M plus the mass added in reproduction (factor R x mass of previous year) plus the growth since last year (growth factor G x mass of previous year)

17 Stock Recruitment Models Objective of model is to predict recruitment (the number of newly born that enter and are noticed in the first year class - 0+ )

18 Stock Recruitment Models 2 Model presumes that recruitment can be predicted on basis of stock in previous year

19 Stock Recruitment Models 3 Model presumes that recruitment increases with increasing stock size, up to a maximum, then recruitment decreases because a stock of increasing size will be more and more limited by food and will produce proportionally fewer new recruits

20 Stock in previous year Recruitment Stock-recruitment model Density-dependent effects

21 Maximum Sustainable Yield Based on idea that a fishery stock will grow at a slower rate over a certain stock size

22 Maximum Sustainable Yield 2 Based on idea that a fishery stock will grow at a slower rate over a certain stock size Idea is to fish the stock down to the population level where growth is maximal

23 Maximum Sustainable Yield 3 Based on idea that a fishery stock will grow at a slower rate over a certain stock size Idea is to fish the stock down to the population level where growth is maximal Leads to management tool to determine fishing pressure

24 Maximum Sustainable Yield 4 Based on idea that a fishery stock will grow at a slower rate over a certain stock size Idea is to fish the stock down to the population level where growth is maximal Leads to management tool to determine fishing pressure Not much evidence that this approach works, even if the theory makes some sense

25 Maximum Sustainable Yield 5 Based on idea that a fishery stock will grow at a slower rate over a certain stock size Idea is to fish the stock down to the population level where growth is maximal Leads to management tool to determine fishing pressure Not much evidence that this approach works, even if the theory makes some sense Problem might be that factors other than simple density dependence affect stock size

26 Fishing Techniques Hooking fishes individually - e.g., long lines with rows of hooks Entangling fishes in nets - e.g., large drift nets, nets towed below the surface and kept open with wooden boards Traps - e.g., baited lobster traps kept on bottom

27 Hooking Fishes Individually Angling Hand line Demersal long line Floating long line

28 Drift nets Set nets Pelagic trawl Purse seine Bottom otter trawl Fishing with nets

29 Stock Reduction - factors Environmental change “Random factors” Overfishing

30 Vulnerable Fisheries Life histories with long generation times Life histories with low fecundity Stocks with confined populations (aggregations or geographic range in a confined area) Resource species that are easily caught

31 Management Problems 1 Fisheries managed by a variety of local and federal agencies

32 Management Problems 2 Fisheries managed by a variety of local and federal agencies Management recommendations not always in best interests of maintaining stock

33 Management Problems 3 Fisheries managed by a variety of local and federal agencies Management recommendations not always in best interests of maintaining stock Some policies backfire - e.g., Magnuson Act of 1976 which extended US coastal fishing zone 200 miles from shore but resulted in extensive deployment of US fishng boats, resulting in overexploitation

34 Management Problems 4 Fisheries managed by a variety of local and federal agencies Management recommendations not always in best interests of maintaining stock Some policies backfire - e.g., Magnuson Act of 1976 which extended US coastal fishing zone 200 miles from shore but resulted in extensive deployment of US fishng boats, resulting in overexploitation Magnuson Act established 8 regiona fishing commissions to help regulate domestic fishing - results good in some cases, bad in others

35 Effects of Overfishing 1 Great reduction of many stocks, e.g., formerly productive Georges Bank, east of New England

36 Effects of Overfishing 2 Great reduction of many stocks, e.g., formerly productive Georges Bank, east of New England Effects concentrated especially on species with vulnerable life cycles (low fecundity, long generation time - e.g., sharks, whales)

37 Effects of Overfishing 3 Great reduction of many stocks, e.g., formerly productive Georges Bank, east of New England Effects concentrated especially on species with vulnerable life cycles (low fecundity, long generation time - e.g., sharks, whales) Collateral effects on the bottom, where bottom trawling continually turns over the bottom, killing epibenthic animals

38 Effects of Overfishing 4 Great reduction of many stocks, e.g., formerly productive Georges Bank, east of New England Effects concentrated especially on species with vulnerable life cycles (low fecundity, long generation time - e.g., sharks, whales) Collateral effects on the bottom, where bottom trawling continually turns over the bottom, killing epibenthic animals Elimination of species at the tops of food chains, which tend to be lower in abundance and have vulnerable life history characteristics

39 GEORGES BANK Atlantic Ocean Cape Cod Year Metric Tons x 10 3 Georges Bank Stock landings Cod Haddock Yellowtail Trends in landings of three major fisheries on Georges Bank on the New England continental shelf

40 Some new management tools Individual transferable quota (ITQ) - licenses are limited in number with quotas for each license, which can be sold Marine Protected Areas (also known as No- Take Areas) - some portion of the stock’s geographic range is closed to fishing - protects spawning grounds, nursery grounds, or minimal crucial habitat size to preserve stock even when fishing is too high

41 Spawning area Juvenile Feeding area Adult feeding area No-take areas Current and dispersal direction Hypothetical No-take Plan

42 Mariculture - Important Factors Desirability as food Uncomplicated reproduction Hardiness Disease resistance High growth rate per unit area (growth efficiency) Readily met food and habitat requirements Monoculture or polyculture Marketability Minimal ecological damage

43 Mussels and Oysters Mussels usually recruit to ropes and poles Placement in areas of high phytoplankton density and water flow Oyster newly settled larvae (spat) collected and then transferred to trays that are suspended from rafts Problem: bivalve diseases, e.g., MSX in oysters - amoeboid protozoan

44 Harmful Algal Blooms (HABs) 1 A variety of toxins, usually produced by species of phytoplankton

45 Harmful Algal Blooms (HABs) 2 A variety of toxins, usually produced by species of phytoplankton Toxins are consumed, along with phytoplankton cells, by resource bivalves, who sequester toxins

46 Harmful Algal Blooms (HABs) 3 A variety of toxins, usually produced by species of phytoplankton Toxins are consumed, along with phytoplankton cells, by resource bivalves, who sequester toxins Toxins are then consumed by people

47 Harmful Algal Blooms (HABs) 4 A variety of toxins, usually produced by species of phytoplankton Toxins are consumed, along with phytoplankton cells, by resource bivalves, who sequester toxins Toxins are then consumed by people Seasonality allows regulation in some cases (e.g., prohibition of exploitation of coastal mollusks in California from May-August)

48 Major HAB types 1 Paralytic Shellfish Poisoning (PSP) - variety of neurotoxins produced by dinoflagellate species of Alexandrium, Gymnodiniums, Pyrodinium - strong neurotoxic effects, respiratory arrest, occasional death Amnesic Shellfish Poisoning (ASP) - domoic acid produced by species of the diatom Pseudonitszchia - causes amnesia, neurological damage, even death

49 Major HAB types 2 Neurotoxic Shelfish Poisoning - caused by brevitoxin, produced by dinoflagellate Gymnodinium breve, can be breathed from aerosols Pfiesteria piscicida - toxin not identified, but causes severe neurotoxic effects, one of many life history stages of this species emerges from the bottom and can attack fish.

50 Spread of HABs 1 Frequency and geographic extent of HABs are increasing Harmful species often affect shellfish physiology as well as humans and may kill entire populations (e.g., killing of bay scallop Argopecten irradians by “brown tide” organism in waters of New York)

51 Spread of HABs 2 Increase may be a result of increasing disturbance and pollution of coastal zone, or more frequent introductions from shipping traffic Increase results in more frequent closures of shellfish beds, fish kills (Pfiesteria), sickness,

52 Seaweed Mariculture Nori - derived from red Porphyra spp., rich in protein, used to wrap sushi, spores collected on nets and grown in estuarine areas Kelps - grown actively in western U.S. coastal waters, harvested for alginates, used in a number of foods Many others, some harvested directly from shore

53 Fish Ranching Marine fish, such as salmon species, are grown in open water tanks Genetic engineering now being used to introduce fast-growth forms Problem - many escape and mix with wild salmon (1/3 of salmon in Norwegian rivers derive from ranched salmon)

54 The End


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