Download Juvenile fish habitats

Habitats of importance to juvenile
fish in the Hauraki Gulf
Darren Parsons (with Mark Morrison, Meredith Lowe & Emma Jones)
Juvenile fish and habitat
Derrick Paull
Juvenile fish and habitat
• Consider the whole life cycle
• Consider locations where you don’t fish for
adults
• Consider impacts that don’t arise from fishing
• USA: Magnuson-Stevens Fishery Conservation
and Management Act 1996 (Essential Fish
Habitat)
Fish ontogeny
Nursery habitat (Beck et al. 2001)
• Spatial disjunction between adult and juvenile
habitat (not all species are nursery
dependent)
• Nursery habitats have: (1) higher density, (2)
greater growth, (3) greater survival
• Leads to a disproportional per unit area
contribution to adult populations
• A bottleneck
Why are nurseries important?
• Complex structure (often biogenic) that
provides: (1) protection from predation,
(2) provision of food
Roger Grace
Nursery habitat in the Hauraki Gulf?
• Information is sparse
• Juveniles small and cryptic
• Some observations from divers, shallow water
beach seine and trawl surveys
• Water clarity, depth, net mesh size and habitat
complexity impinge on these methods
Upper estuary,
muddy
Hauraki Gulf important,
particular associations
and locations unknown
Estuarine flats
Abundant throughout
Gulf, flotsam
of habitats from Hauraki
upper
for early juveniles
Summary: a range
estuaries, to coastal environments, rocky
reefs, bare sediments and offshore
Biogenic
habitats in
flotsam.
Specific habitat associations,
Brown algae on
estuaries and on the
rocky reefs
coast locations and mechanisms generally
poorly understood
Offshore
pelagic nursery,
flotsam
Images from Malcolm Francis
Non-Hauraki
Gulf nurseries
Clear sandy
estuaries and
surf zone
Seagrass
Matheson and Whadwa 2012
Seagrass a ‘declining species’
Matheson and Whadwa 2012
Seagrass a ‘declining species’
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Roger Grace
Whangarei Harbour
Morrison et al. 2003
Seagrass as a nursery
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Crispin Middleton
Snapper
Pipefish
Trevally
Spotty
Triplefin
Parore
Goatfish
Jack mackerel
Exquisite goby
Leatherjacket
Seagrass juvenile snapper
• Response to blade density
• Response to landscape
features
• Seagrass odour attractive to
snapper larvae (Radford et al. 2012)
50
40
30
Abundance (no. of individuals)
20
10
0
Parua Bay
Takahiwai
Snake east
MacDonald
Site
Current strength
Snake west
Snake south
What about the Hauraki Gulf?
• All of the above research from outside of the
Gulf
• Subtidal seagrass once abundant in
Waitemata, but largely gone by the 1930’s
(Powell 1937)
• Seagrass now very restricted in the Hauraki
Gulf
What about the Hauraki Gulf?
What about the Hauraki Gulf?
• All of the above research from outside of the
Gulf
• Subtidal seagrass once abundant in
Waitemata, but largely gone by the 1930’s
(Powell 1937)
• Seagrass now very restricted in the Hauraki
Gulf
• Where do Hauraki Gulf snapper come from?
Coastal
habitats for
juvenile
snapper?
Coastal habitats for juvenile snapper?
Ian McLeod
Roger Grace
Paul 2012
Chris Battershil
Habitat restoration
Are environmental
conditions suitable
for restoration to
succeed?
Summary
• Need to consider all the life cycle requirements of the
fish we value
• Juvenile nurseries important because they are a
bottleneck – they are disproportionately important
• Information on the nursery habitat requirements very
poor for most fishes
• Especially true for snapper in the Hauraki Gulf
• Important information for prioritising management
• A prerequisite for restoration is suitable environmental
conditions