L12 Marine Fisheries

Question 1

When did fishing begin, timeline of fishing.

Answer 1

Since man evolved
evidence in SA of huge piles of seashells - neolithic
Earliest evidence of hooks associated with bones of pelagic species from 42,000 years ago.
Extensive exploitation of marine fisheries started 1000 years ago. Before, was focussed on FW fisheries). Seen from examination of fish bone assemblages. FW maybe overexploited so shift to marine.

Question 2

Globally, what is the trend in fishery landings?

Answer 2

risen steadily since 1950s but don ‘t accurately reflect the number of fish caught. Often undersized fish are discarded at sea and some landings are unreported.
Dominated by a handful of species eg 5 species make up 15% of global landings.

Question 3

Which 5 species make up 15% of global landings?

Answer 3

Chilean jack mackerel
Atlantic herring
Chub mackerel
Peruvian anchovy
Alaskan pollock

Question 4

after 1990s what are the global trends in fishery landings?

Answer 4

most level off, then start to decline due to effects of overfishing starting to kick in.
China’s statistics are false, as Possible that chinese fishermen lie about catches to seem more successful, so the true global rate may actually be more declining.

Question 5

Where are fisheries?

Answer 5

Usually kept to continental shelves - v productive areas of epipelagic. Upwelling is in areas off SW coast of africa and peru.
<40% of worlds fisheries are deeper than 200m.

Question 6

what are some passive and active fishing methods?

Answer 6

Passive - Gill nets, entangle fish by gills.
Long lines - With thousands of hooks, baited pots and traps.
Active - Purse seine, encircles pelagic species.
Trawl gear, dragged along behind boats. Otter trawls are weighted down and kept open, beam trawls have a fixed beam next to the sea floor.
Blast fishing, harpoons and Spears

Question 7

Describe trawling effort in UK waters

Answer 7

In the North sea, VMS (vessel monitoring system) estimated that every square foot has been trawled 3-4 x each year. Intensive trawling effort, a\s all accessible grounds exploited in UK waters.

Question 8

What cased stocks of North sea cod to decline, and what is the trend?

Answer 8

Fishing pressure increased until 2000 when realisation of declining stocks getting critically low, caused fishing pressure to drop by almost half. Afterwards, signs of stock biomass gradually increasing.
Used body size as an indicator of Fishing pressure, as fishermen usually take the larger fish.

Question 9

How has industrialisation affected fishing?

Answer 9

Over the 20th century switch in fishing methods from sail trawlers to steam then motor power, increasing efficiency. This opened up new areas for exploitation.

Question 10

How does size of fish compare to the past?

Answer 10

See otoliths of fossilised Neolithic cod, to reconstruct population sizes and compare to now. Modern fished individuals are about 10cm. Smaller than 4500 years ago.
Similar trend in analyses of pelagic species eg tuna, sailfish, long line catches per unit effort, from 1950 - 2000.

Question 11

How has predator biomass affected other species and compare to the past?

Answer 11

spatial patterns of predator biomass show decline in pelagic catches.
Large predatory biomass today is estimated to be only 10% of what it was pre industrial levels

Question 12

What can you limit to manage a fishery?

Answer 12

• Total catch and close fishery when catch is reached
• length of fisheing season
• areas open for fishing
• No. boats permitted to fish and catches per boat
• gear size and type, affects size of fish caught.
• fishing methods
• quotas for individual species.

Question 13

What is the MSY?

Answer 13

Maximum sustainable yeild
Highest catch that can be maintained year after year without affecting stock.
Too little fishing = underutilized catch
Too much fishing = overfished area.

Question 14

How is MSY estimated?

Answer 14

Using afunction of the population, incorportating: size of individuals in pop, birth and natural death rates, age of maturity.

Question 15

How does MSY influence politics?

Answer 15

Can use MSY to estimate amount of fish to harvest in a sustainable fishery. - Hasn’t always worked well due to lack of political will as reccommendations often ignored by european ministers. Since 2013, discards and landings >MSY have been prohibited, so we are now moving forward.

Question 16

What is a problem with fisheries management regarding determining the real abundance in fisheries?

Answer 16

1. Determining the real abundance of is an issue as most stocks aren’t surveyed independently from fisheries so biased. Surveys are expensive and often not feasible as data requires thorough analysis. Often stock assessment relies on landings alone.

Question 17

why can using landings alone be a struggle when trying to determine the real abundance of fisheries?

Answer 17

using landings to measure fish stock is entirely dependent on gear and methods staying constant, with consistent locations by fishers.
If not consistent, worried that fisherman may be ‘following the fish’ and get high catches despite the dwindling population.
Eg. NW altantic cod were abundant and successful fisheries, then collapsed in 1992 and not recovered. Cod pop was diminishing but unnoticed as remaining cod aggregated and fisheries maintained high catches.

Question 18

How were Chinas catches misreported?

Answer 18

FAO grossly misreported chinas catches. Almost no long haul catches reported to FAO despite having largest international fleet in the world

Question 19

What is the extent of mislabelled fish?

Answer 19

Mislabelled at sea and after landing.
DNA based species identification of fresh and smoked fish showed 25% of all fish sampled were mislabelled, and 82% of smoked fish were mislabelled.

Question 20

What are the 4 major issues with fishery management?

Answer 20

1. Determining the real abundance of fish
2. Ensuring constant behaviour of fisherman
3. Ensuring landed fish arent unreported
4. Mislabelling

Question 21

What is a more successful management of fisheries in poorly governed places?

Answer 21

Most fisheries dont have resources to enforce regulations, and is managed top down by regional government, will develop cheating culture which will devaluate gov. work.
Co management btw local communities and authorities is more successful.

Question 22

Where is fishery management most successful?

Answer 22

in areas of high HDI, industrial fishing and benthic/demersal fisheries and offshore ecosystems.

Question 23

What are the most and least important factors in successful leadership?

Answer 23

Strong leadership, strong quotas, social cohesion, protected areas.
Least important: scientific advice, landing success and restocking

Question 24

Which is the most damaging fisheries to the ecosystem, and

Answer 24

Trawlers are damaging to benthos. Taxa on sandy seabeds are adapted to stress by waves so has less impact, but on hard bottom of rocky biogenic habitats, trawling gives long term damage.

Question 25

describe fishing on seamounts

Answer 25

Technological advances and declining near shore stocks have allowed seamounts to be heavily fished on for past 25 years. Deep water coral is rapidly destroyed. Coral bycatch carbon is dated to >5000 years old.

Question 26

Which species are most affected by bycatch?

Answer 26

Some of the non target species are landed and sold, others are just discarded.
European skates undergone decline due to bycatch. Large low fecundity species eg elasmobranches are affected very seriously.
Bycatch also includes seabirds which dive down after baited hooks.

Question 27

Two other damaging fishing techniquies

Answer 27

Dynamite fishing - extensive use in SE asia, kills juvenile and non target species and destroys the reef.
Ghost fishing - lost hooks, nets and lines continue to catch fish for years, as synthetic material is very durable. the caught fish act as bait for larger predators.

Question 28

How has fishing shaped fish evolution?

Answer 28

• Size selective, removed largest individuals. maybe artificial selection for early maturing fish, faster growing but only to a small size?
• Strong evidence that genetic diversity is effected in stocks. eg 1940-90 NZ snapper landings increased but spawning stock biomass decreases. Loss of allelic diversity in samples collected 1952-98.

Question 29

What is an experiment

Answer 29

Conover and Munch - investigated to see if size selective harvesting leads to loss of late maturing late growing phenotypes?
Stocked atlantic silverside under 3 harvesting treatments
T1 - Large harvested, largest 10% removed.
T2 - Small harvested, smallest 90% removed
T3 - random
survivors weighed and measured, 100 surviving breed for 4 generations.
Total weight and mean weight differed between treatments. Large harvesting declined in both response variables. Small harvesting increased in weight variables.

Question 30

What is a portfolio?

Answer 30

lifehistory diversity

individuals of different ages and source populations

Question 31

Why is a diverse portfolio beneficial for overall population stability? and example

Answer 31

helps buffer effects of local environmental change.
Eg Bristol Bay, Alaska, Sockeye salmon stock.
display natal philopatry, thestock returning to FW to breed is made of different ages from different natal water bodies.
Greater values of N2 in sediment of natal habitat = more salmon. until 1800, most natal habitats fluctuated in salmon abundance and populations doing differently to each other. Stock in bristol bay made of more and less successful populations but overall balance is healthy.

Question 32

when did stocks start to rebuild

Answer 32

1980s - 90s when overfising was recognised.

Question 33

What is a fast growing area of food production?

Answer 33

Aquaculture - meets needs of people in developing countries. Marine aquaculture is expensive and difficult, focused on high value species.
Worries of release of invasive species, habitat destruction and source of feed.