topic 17 -Conservation: Fisheries Flashcards
Conservation practices are based on a
thorough understanding of the principles of ecology
conservation must integrate
ecology with social, political and economic systems
focus: harvesting species
Atlantic Cod
length and weight ?
life span?
maturity?
how many eggs?
2 meters and 200+ pounds
25 years lifespan
2-4 years
females can lay millions of eggs
Canadian cod fisheries are centered around
the grand banks
Cod Populations
originally discovered by?
discovered by John Cabot 500 years ago
so abundant you could walk on their backs, thought to be infinite
Declines in cod across their range including
Baltic Sea and especially coast of Newfoundland and labrador
cod landings 1950s 1977 1991 1992
50s lots of cod, factory freezer trawlers
77 200 mile limit EEZ
91 cold year
92 fishing moratorium
in the 1950s, technology allowed fishermen to fish by
trawling a large area to a deep depth for longer times
in the 1960s, technology allowed fishermen to be equipped with
powerful trawlers equipped with radar, electronic navigation systems and sonar which allowed crews to catch fish with unparalleled success
since 1977 (200 mile limit Exclusive Economic Zone)
excluded foreign nations from fishing in Canadian waters
Canadian Government set the annual harvest rate based on information from scientists
After WW2 scientists overestimated N-set annual harvest rates too high, the estimates of N were
based on commercial catch rates (assumed high catch=high N)
Aggregated (dispersion) during spawning allowed
high catches while population was declining fast
underestimated mortality from fishery
catches misreported
large discarding in by-catch when harvesting other species
in 1980s annual harvest rates were higher than scientists recommended due to
fishers lobbied hard for higher harvest rates, attitude was that cod was a super-abundant resource
Government maintained annual harvest rates higher than recommended to avoid political suicide
1992 population had declined to
99% of its original level
1995 saw a slight increase in population size therefore
the government reopened a small inshore fishery despite strong opposition from scientists
2003 fishery closed again population declined to
99.9% of its original level, recommended to be listed as an Endangered species under Canadas Species At Risk Act (SARA)
1992 there was a fishing….
which lead to how many unemployed
jobs lost
moratorium, fishery closed to allow population to recover
19000 fishers and plant workers became unemployed
20000 other jobs lost (100s of small communities cod was only employer)
what did fishers do when work was lost
TAGS program -social assistance
retraining programs
Emigration of people out of NL to find work
Fishers shifted to harvest other species
By-catch
unused catch discarded at sea -target and non target species
ex shrimp trawl species 3:1 to 20:1 by-catch: landed
misreported and illegal catch and by catch, hard to estimate population declines
cod killed by nets or die when brought to surface (returned to ocean dead)
why are food webs complex?
need to more about how species interact to understand how adding/removing a species will influence community structure and to conserve marine biodiversity
Population resilience
what does it combine
rate at which population returns to equilibrium size (k) after a population crash
combines the age structure, spatial structure and life history characteristics of a population
r-selected resilience
invest heavily into reproduction (high r) shorter potential time to return to K again if population is reduced (quick recovery, high resilience)
k-selected resilience (cod)
invest heavily into growth/survival (low r) longer potential time to return to K again if the population is reduced (slow recovery, low resilience)
other problems with small population: inbreeding, genetic drift
