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What Are They Doing Down There: An Investigation of Multiple Paternity in a Deep-Sea Shark, Melissa Nehmens [et al.]

What Are They Doing Down There: An Investigation of Multiple Paternity in a Deep-Sea Shark, Melissa Nehmens [et al.]

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E1/ Diadromous fish of the Indo

Pacific: Biogeography, ecology and

conservation



332



Bullied bullies: Competition shifts dietary

niches in Gobiomorphus cotidianus

Marine Richarson

1



∗ 1



University of Otago - Department of Zoology – PO Box 56 340 Great King St Dunedin 9016, New

Zealand



Intraspecific ecological niche variation has long been suspected of shaping population dynamics, with potentially large effects at the ecosystem level. While recent efforts have uncovered

mounting evidence of individual specialisation across the animal kingdom, few have focused on

the effects of interspecific interactions on individual variation. The common bully (Gobiomorphus cotidianus) is a small New Zealand native fish which exhibits moderate levels of individual

specialisation despite a generalised diet at the population level. The introduced Eurasian perch

(Perca fluviatilis) is a competitor and size dependent predator of the species. Juvenile perch

exhibit dietary niche overlap with bullies: while both species display different foraging strategies, they tend to prey on the same pool of pelagic and benthic invertebrates. We hypothesised

that (1) competition with juvenile perch (TL< 150 mm) and with conspecifics induced consistent dietary shifts in individual bullies, and (2) that these effects were modulated depending on

the nature of the competitor. We subjected individually marked common bullies to different

competition levels in experimental mesocosms, with low competition treatments compared to

treatments with elevated intraspecific or interspecific competition. Repeated diet measures were

conducted over 14 weeks in order to assess individual dietary niches. Preliminary results indicate

that intra- and interspecific competition have similar impacts on fitness (growth rate), but that

the nature of competition seems to drive different types of shifts in individual dietary preferences. These results confirm the importance of integrating individual variation when evaluating

a population’s response to a competing species.







Speaker



333



Complex patterns of population connectivity

in a New Zealand amphidromous galaxiid

Jason Augspurger 1 , Matt Jarvis 1 , Graham Wallis 1 , Travis Ingram 1 ,

Malcolm Reid 1 , Gerry Closs ∗ 1

1



University of Otago – PO Box 56, Dunedin, New Zealand



Life-history requirements play a key role in determining species distributions and population

structuring. Many studies evaluate the role of adult requirements when predicting population

structure, but very few incorporate the role of early life-history, which is usually the most vulnerable, and therefore limiting, phase of life-history. It is also the stage during which population

connectivity most often occurs. A combination of genetic, otolith microchemical, and larval sampling approaches were used to explore long- and short-term patterns of population structuring

in marine and land-locked (lake) populations of Galaxias brevipinnis. Landlocked populations

of Galaxias brevipinnis were found to be genetically diverging from diadromous populations and

each other, despite no obvious physical barriers to population connectivity and close proximity.

On shorter timescales, catchment level meta-populations were formed within lake and coastal

populations. Additional studies have indicated that larvae are strongly rheotaxic, potentially

providing a behavioural mechanism responsible for both long-term divergence and short term

meta-population structuring patterns seen here. These results suggest that management of G.

brevipinnis must consider both long term patterns resulting in evolutionary divergence of nondiadromous populations, as well as the short term catchment-level isolation resulting in distinct

ecological populations in both diadromous and non-diadromous populations.







Speaker



334



Conservation and management of New

Zealand’s diadromous galaxias

Jane Goodman



∗ 1



, David West 2 , Gerard Closs 3 , Travis Ingram



3



1



3



Department of Conservation and University of Otago – Monro State Building 186 Bridge Street

Nelson 7010, New Zealand

2

Department of Conservation – Level 3 Grand Central 161 Cashel Street Christchurch 8011, New

Zealand

University of Otago – Department of Zoology 340 Great King Street PO Box 56 Dunedin 9054, New

Zealand



New Zealand has five species of diadromous galaxias. Four species are listed in the New

Zealand Threat Classification System as threatened or at risk – shortjaw kokopu (Nationally

Vulnerable), giant kokopu (Declining), koaro (Declining), inanga (Declining). The fifth species,

banded kokopu is listed as not threatened. The juveniles of these species are harvested annually

in New Zealand’s whitebait fishery which is managed by way of regulations by the Department

of Conservation.

There has been a decline in abundance of all the diadromous galaxias as well as a geographical

contraction in their location. The decline is hard to attribute to any one factor especially given

we don’t have any overall trend monitoring data, however extensive changes to waterways including, removal of forest, draining of wetlands, degradation of river estuaries, intensification of

farmland, decreasing water quality, the introduction of exotic species and fishing pressure all to

some extent impact on the species and cumulatively the effect has been significant.

In the past 30 to 40 years our understanding of these species has increased enormously, however

there are still big gaps in our understanding, particularly in relation to larval habitat and food

requirements, influences of the marine environment on population dynamics, location of spawning habitats, and the genetic structure of populations or ‘stocks’ around the country.

The purpose of our research is to

To investigate how fisheries based on juvenile diadromous fish are managed internationally

To increase understanding of migratory galaxias dispersal, recruitment and distribution by investigating genetic structure and otolith microchemistry

This presentation outlines the current status of New Zealand’s diadromous galaxias, how the

whitebait fishery is managed; and presents our preliminary findings in relation to international

fisheries management models for juvenile diadromous fish and the genetic structure of four of

the five diadromous galaxias species around New Zealand.







Speaker



335



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