Pelagic Fisheries Flashcards
Pelagic Fisheries
Fish within the water column – not associated with the bottom
Water column can be shallow or very deep
What are the water column layers based on the types of fisheries?
- Zooplankton
- Forage Fishes
- Large Pelagics
- Demersals
- Benthic Invertebrates
Do fish mainly stay within their water column zone?
No, there is spatial relationships between different species within multiple water columns.
- Life history stage dynamic as well.
What distinguishes between large forage fish and large pelagic fish?
Movement
Biological Characteristics of Large Pelagic
Most are top level predators
Feed on smaller fish and squid
High metabolic rates
Several species maintain elevated temperatures in some body regions
Highly migratory
Life History Biological Characteristics of Large Pelagic
High fecundity
Broadcast spawning over a large geographic area (except bluefin tuna)
Rapid growth
Most species reach sexual maturity at 2 – 4 years (except bluefin tuna)
Can be relatively long-lived (6 – 20+ years)
What species of pelagic fish is excluded from the life history?
Pelagic sharks
Fecundity
the ability to produce an abundance of offspring or new growth
Surface Fisheries Gear used for Pelagic
Purse seine (w/ & w/o FADs)
Baitboat (w/ & w/o FADs)
Trolling
Drift gill net
Recreational fishery
FAD
Fish aggerated devices
Subsurface fisheries gear types
Pelagic longline
What are the major species within the pelagic fishery
- Tuna
- Wahoo
-Swordfish - Billfishes
-Dolphin/Mahi Mahi
What are the two pelagic shark species that are considered within this fishery?
- Shortfin mako
-Blue shark
What is the commonality between all of the species within the Scombriformes?
Not exclusive but most are highly migratory
What is one of the most valuable fish on the market?
Bluefin Tuna (some sell for millions of dollars)
What is the main family of the pelagic fishery?
Scombriformes
What are the seven families of the Scombriformes?
Scombrolabracidae – escolar
Sphyraenidae - barracudas
Gempylidae - snake mackerels
Trichiuridae - cutlassfishes
Scombridae – tunas
Xiphiidae - swordfishes
Istiophoridae - billfishes
Characteristics of the Scombridae family
“Two” dorsal fins, depressible into grooves
Finlets present
Scales small, cycloid
Some are endothermic (produce their own body heat)
What are the characteristics of the Istophoridae & Xiphiidae
Elongate premaxillary bill (rostrum)
Finlets absent
Dorsal fin far anterior
Extremely well-developed zygapophyses
zygapophyses
one of the two paired processes of a vertebra that interlock it with the adjacent vertebrae.
What is the commonality between Scombridae and Istiophoridae/Xiphiidae?
Fast swimming - Can tuck all of the fins in to eliminate any drag.
What Scombridae species has the broadest thermal tolerance?
Atlantic Bluefin Tuna
Atlantic Bluefin Tune Biology
- Max size/ age - 679 kg; 300+ cm FL; 35+ years
- Oceanodromous
- Significant time at surface but capable of diving to 800 m
- Juveniles - shallower and closer to shore in summer
An interesting fact about Atlantic Bluefin Tuna
There are two stocks within the Atlantic—one with a Gulf of Mexico Spawning Ground and the eastern stock with a Mediterranean spawning ground. These stocks differ in maturity schedules.
- W - 50% at age 4
- E - 50% at age 5-12
Atlantic Bluefin Tuna : Eastern Stock/Fishery
- Centuries of fishing with traps in the Mediterranean
- Norway & Germany developed a purse seine fishery in the 1950s and 60s
- Led to major overfishing
Why was the purse seine technique so detrimental to the fish stock for Bigeye Tuna?
They are a mixed school species. Similar size species school together. LL is more selective. Purse Seine will get all species within the net. It is catching the immature individuals.
Bigeye Tuna Biology
- max size/age - 200 kg; 300+ cm FL; 16 years
- Oceanodromous, but the relatively little long-distance movement
- Atlantic is genetically distinct
Changes in the Bigeye Tuna Fishery
Catches of juvenile bigeye increase as skipjack fishery increases (juvenile bigeye co-school) with skipjack
Increased purse seine fishing on FADs which tend to have the smallest bigeye
Leads to growth overfishing of bigeye tuna
Change in the selectivity of the fishery results in lower MSYs
Maximum Sustainable Yield
The highest possible annual catch that can be sustained over time, by keeping the stock at the level producing maximum growth
Growth Overfishing
is when fish are harvested before they reach the size where yield per recruit is optimized; the weight and value of the catch may be reduced
Swordfish Biology
- Max age is difficult to determine (Otoliths are often too small to determine proper age)
-Distributed worldwide - migrate to cooler waters in summer for feeding - Cyclical movements vs. east to west
A lot of genetic separation – little exchange between the north Atlantic and south Atlantic – leads to a good stock structure.
Global Swordfish Production
-Fishery took off in the 1970’s
-North Atlantic swordfish was significantly overfished and lead to a crash in the 1990s
-Both NA and SA stocks are rebuilding. North is considered not overfished but the south still considered overfished.
