Porbeagle Flashcards
Describe the relationship between the NW and NE Atlantic porbeagle (movement, genetics).
- No genetic difference between the populations, indicating some genetic exchange
- Only one documented instance of transatlantic migration
- Assess as different populations in some cases given lack of significant movement and different management regimes
Describe the first record of transatlantic migration by porbeagle.
- 20 pound female first capture in Ireland
- Recaptured over 10 years later at over 200 pounds, 185 cm TL by Faroe Island vessel south of Grand Banks
Describe the use of Irish waters by porbeagles.
- summer aggregation site for juveniles
- seasonal site fidelity for juveniles
- juveniles return to nearby locations between years
- evidence for size- or age-based spatial segregation
high seas
international open waters
Approximately what percentage of time is spent on high seas where they are largely unregulated and unmonitored?
Approximately 92% of time
regional fisheries management organizations (RFMOs)
quai-cooperative alliances among countries that agree to work together toward a common goal
-ex: ICCAT
When are spatial or seasonal fishery closures not effective?
when the target species and bycatch species share the similar habitat and prey items
What fishery accounts for the most shark bycatch?
Pelagic longline fisheries
How was overall mortality estimated by Campana et al. 2016?
sum of PRM for injured and healthy sharks (weighted by the relative frequency of each category) plus frequency of dead sharks (capture mortalities)
What was the hooking mortality of porbeagles in the PLL fishery estimated by Campana et al. 2016?
44%
What was the PRM for healthy porbeagles caught in PLL fishery by Campana et al. 2016?
10%
What was the PRM for injured porbeagles caught in PLL fishery by Campana et al. 2016?
75%
What was the overall PRM for porbeagles in the PLL by Campana et al. 2016?
27.2%
Which species had the highest total fishing mortality (mako, blue, porbeagle) by Campana et al. 2016?
porbeagle
What was the total fishing mortality for porbeagles in PLL fishery by Campana et al. 2016?
59.1%
Why might porbeagles be most effected by PLL fishing in Campana et al. 2016?
- lamnids have high MR and high O2 requirements
- reduced ability to ram ventilate while hooked may not provide enough O2
What was the seasonal migration of mature female porbeagles in the southern hemisphere (Francis et al. 2015)?
- moved to lower latitudes during winter and spring and higher latitudes during summer
- hypothesized to have reproductive source
Explain the vertical movement pattern of porbeagles in the southern hemisphere (Francis et al. 2015)?
Diel vertical migration
- dive deeper during the day
- diel vertical migration less consistent when in shallower waters above the continental shelf
How did Francis et al. 2015 suggest the southern hemisphere could reduce porbeagle bycatch?
limit PLL fishing to daylight hours when porbeagles are too deep to be caught
Describe the relationship between the N Atlantic and southern Hemisphere porbeagle.
- genetically and biologically different
- southern Hemisphere population grows smaller, slower, and is longer-lived
- tropics at low latitudes may be a thermal barrier to population mixing
What is the male size at maturity in NW Atlantic (Jensen et al. 2002)?
- between 162-185 cm FL
- 174 cm FL is size at 50% maturity
What is the male age at maturity for the NW Atlantic (Jensen et al. 2002)?
8 years
What is the female size at maturity in NW Atlantic (Jensen et al. 2002)?
- between 210-230 cm FL
- 218 cm FL is size at 50% maturity
What is the female age at maturity in NW Atlantic (Jensen et al. 2002)?
13 years
When is the expected mating season in the NW Atlantic (Jensen et al. 2002)?
Fall (September-November)
When is the expected pupping season in the NW Atlantic (Jensen et al. 2002)?
Spring (April-June)
What is the average litter size in the NW Atlantic (Jensen et al. 2002)?
4 pups (range 3-6)
What did Jensen et al. (2002) suggested the reproductive cycle was in the NW Atlantic? Why
1 year
-most/all females were reproductively active
How long is gestation in the NW Atlantic (Jensen et al. 2002)?
8-9 months
What is the geographic range of porbeagles in the NW Atlantic?
Flemish Cap and Grand Banks to GOM (rarely south to NJ) and the Sargasso Sea
What was the size at 50% maturity for males based on in the NW Atlantic (Jensen et al. 2002)?
clasper condition
What was the depth range of porbeagles in the NE Atlantic during the winter (Saunders et al. 2011)?
0-700 m
What was the temp range of porbeagles in the winter in the NE Atlantic (Saunders et al. 2011)?
9-17C
Describe the vertical movement behaviors in the NE Atlantic winter (Saunders et al. 2011).
- inter-individual variation
- shallower at night than day
- transition in diving behavior when moved off shelf
Describe migration pattern of porbeagles in winter in NE Atlantic (Saunders et al. 2011).
Located at shelf break or off shelf areas during autumn and winter, some individuals migrate south
What may drive residency behavior in porbeagles?
High localized food availability
What might drive migrations of porbeagles?
- searching for better feeding environment
- searching for mates
- gestation grounds
How does vertical movement change when porbeagles move off the shelf?
stay deeper in the water column and rarely come to surface
What could be the driver of diel vertical migration for porbeagles?
distribution of planktivorous fish that feed on diel vertically migrating zooplankton
What was the size range of porbeagles tagged by Skomal et al. 2021?
128-154 cm FL
Describe the horizontal migration of juvenile porbeagles in the NW Atlantic by Skomal et al. 2021.
Shelf oriented in summer and fall with more offshore movement in winter. Started to move back onto the shelf in Spring.
What was the temperature range of porbeagles tagged by Skomal et al. 2021?
2-26C but 97% of time spent between 6-20C
Describe the seasonal vertical movement patterns of porbeagles tagged by Skomal et al. 2021.
- Shallower distribution when on shelf with less pattern
- Diel vertical migration when offshore, some stayed deeper than 200 m (when in warm waters of Gulf Stream), others stayed above 200 m (when north of Gulf Strem)
What factors are suspected to drive juvenile porbeagle seasonal horizontal and vertical movements in NW Atlantic (Skomal et al. 2021)?
- foraging behavior mediated by temperature
- although they have broad thermal tolerance, likely movements driven by optimal temperature range
Why should the western and eastern North Atlantic porbeagle be managed as two separate stocks when they are genetically related?
- migration rates are low (2-12 individuals per year) enough that recruitment recovery from the other side of the ocean would not likely occur
- a much higher number of individuals migrating would be required to promote recovery of a depleted stock
