Fishery Management

1
Fishery Management

• Fishing is extractive
• Removes choices organisms - fine-ing
• Changes food web structure
• The human condition provides little incentive to
  maintain sustainable stocks
• Need way to control ourselves

2
Ecosystem Effects

• We take the best tasting, most profitable fish
  first
• Worldwide depletion of predatory fish
• 10 of pre-industrial carrying capacity
• What was the baseline???
• Myers Worm Nature 2003

3
Fine-ing
Catch per unit effort (CPUE)
4
Fine-ing
Spatial patterns of relative predator biomass in
1952 (a), 1958 (b), 1964 (c) and 1980 (d). Color
codes depict the number of fish caught per 100
hooks on pelagic longlines set by the Japanese
fleet.
5
Fine-ing
Compensation in exploited fish communities. a,
Oceanic billfish community in the tropical
Atlantic, showing the catch per 100 hooks
(c.p.h.h.) of blue marlin (Makaira nigricans
solid circles, solid line), sailfish (Istiophorus
platypterus open triangles, dashed line) and
swordfish (Xiphias gladius open circles, dotted
line). b, Demersal fish community on the Southern
Grand Banks, showing the biomass of codfishes
(Gadidae solid circles, solid line) and
flatfishes (Pleuronectidae open circles, dotted
line).
6
Fine - ing

• We take the best tasting, most profitable fish
  first
• Worldwide depletion of predatory fish
• 10 of pre-industrial carrying capacity
• What was the baseline???
• Removing the top-level predators alters the
  structure of the marine food web

7
Fishing down the food chain

• Fishing occurs further down the food chain
• Long-lived, high trophic, piscivorous bottom fish
  shift to short-lived, low trophic level
  invertebrates and planktivorous pelagic fish
• Leads at first to increased yields but appears to
  be unsustainable
• Most pronounced in Northern Hemisphere
• Pauly et al 1998 - Science

8
Fishing down the food chain
Marine
inland
9
Fishing down the food chain
NW Central Atlantic
North Pacific
NE Atlantic
Mediterranean Sea
10
Fishing down the food chain
South Pacific
Antarctica
11
Fishing down the food chain

• Fishing occurs further down the food chain
• Long-lived, high trophic, piscivorous bottom fish
  shift to short-lived, low trophic level
  invertebrates and planktivorous pelagic fish
• Leads at first to increased yields but appears to
  be unsustainable
• Most pronounced in Northern Hemisphere
• Pauly et al 1998 - Science

12
Otter-Kelp-Urchin Food Web
Otters are the keystone predator of this food web
13
Otter-Kelp-Urchin Food Web
Removing otters affects food web structure
14
Kelp-Otter-Urchin-Orca

• Long time records of kelp otter records in
  Aleutian Alaskan coastal waters
• Otters kelp increase as urchin decreases and
  vice-versa
• Top-down control by apex predator
• Concept of a trophic cascade

15
The Otter Kelp Urchin Food Web
Trophic cascade Estes et al 1998
16
Otter Kelp Urchin Food Web
Clam Lagoon
Kuluk Bay
17
Kelp-Otter-Urchin-Orca

• Long time records of kelp otter records in
  Aleutian Alaskan coastal waters
• Otters kelp increase as urchin decreases and
  vice-versa
• Top-down control by apex predator
• Speculates that food switching by orcas from fish
  to nearshore mammals

18
Food Web Responses
Historical analysis of marine food webs Before
after the anthrocene Food webs without apex
predators Jackson et al. 2001
19
Food Web Responses
Removal of mammals harvest of other organisms
creates trophic cascade
20
Food Web Responses
Relative importance of grazing inverts
vertebrates affect relative importance of corals
algae
21
Food Web Responses
22
Evidence of Food Web Responses
Atlantic cod
Caribbean corals
Chesapeake Oysters
23
Anthropogenic Disturbances
24
Historical Overfishing

• Removal of key predator species affect the
  functioning of ecosystems
• Evidence in the size of components in historical
  record
• Authors state that overfishing precedes all other
  disturbances in coastal ecosystems