Susan W. Kim

A length-based Bayesian stock assessment model for the New Zealand abalone Haliotis iris

We describe a length-based Bayesian model for stock assessment of the New Zealand abalone Haliotis iris (paua). We fitted the model to five data sets: catch-per-unit-effort (CPUE) and a fishery-independent survey index, proportions-at-length from both commercial catch sampling and population surveys, and tag–recapture data. We estimated a common component of error and used iterative re-weighting of the data sets to balance the residuals, removing the arbitrary data set weightings used in previous assessments. Estimates at the mode of the joint posterior distribution were used to explore sensitivity of the results to model assumptions and input data; the assessment itself was based on marginal posterior distributions estimated from Markov chain–Monte Carlo simulation. Assessments are presented for two stocks in the south of New Zealand. One may be recovering after recent catch reductions; the other is over-exploited and likely to decline further. Assessment for the first stock was robust; assessment for the second stock was sensitive to the CPUE data and may be too optimistic. We discuss future directions and potential problems with this approach.

Climatic Influences on the Flowering Phenology of Four Eucalypts: A GAMLSS Approach

This chapter represents one of the first attempts to utilize phenological data to detect non-linear responses of flowering to climate change using GAMLSS. We use the flowering of four species (Eucalyptus leucoxylon, E. microcarpa, E. polyanthemos and E. tricarpa) as a case study. Regardless of cyclicity of flowering over time, this study shows that each species flowering is significantly influenced by temperature and this effect is non-linear. Stepwise GAMLSS showed that the main temperature driver of E. leucoxylon is minimum temperature (P<0.0001), maximum temperature for E. polyanthemos (P<0.0001), both minimum and maximum temperature (P<0.0001) for E. tricarpa, and mean temperature for E. microcarpa (P<0.0001). Rainfall was not a significant predictor of flowering. GAMLSS allowed for identification of upper/lower thresholds of temperature for flowering commencement/cessation; for the estimation of long and short-term non-linear effects of climate, and the identification of lagged cyclic effects of previous flowering.

Demographic variation in the New Zealand abalone Haliotis iris

Growth data for the New Zealand abalone Haliotis iris were collected from 30 sites around the New Zealand coast by tag–recapture methods. Most data were collected to provide input into abalone stock assessments within discrete management areas, but had not been examined to determine the nature or extent of any large-scale patterns that might be useful to fishery managers. Sites spanned more than 10° of latitude and were subject to a large range of wave energies and temperatures. Mean monthly sea surface temperature (SST) and wave energy were estimated for each site and a generalised linear regression model was used to examine the relationship between variables. Size-at-maturity was also examined at ten sites. Initial length of abalone explained 35% of the variation in incremental growth, and a further 19% was explained by maximum SST, which also explained 60% of the variation in asymptotic length. Fastest growth was generally in areas with lower mean monthly maximum SST, and sites with the slowest growth had the highest mean monthly maximum SST. Size-at-maturity decreased with increasing temperature. The implications of these broad patterns upon abalone fisheries management strategies are discussed.

Can additional abundance indices improve harvest control rules for New Zealand rock lobster (Jasus edwardsii) fisheries

Abstract Although New Zealand rock lobster (Jasus edwardsii) fisheries can be assessed with a sophisticated Bayesian length‐based model, these assessments are expensive and time consuming; they cannot be conducted for each area every year. Harvest control rules are increasingly important management tools in New Zealand rock lobster fisheries. Recent work has developed and evaluated procedures for rebuilding or maintaining lobster stocks based on criteria agreed by stakeholders. Most management procedures depend on a single abundance index, often catch per unit of effort (CPUE). When management procedures react slowly to changes in vulnerable biomass, allowable catches get out of phase with the stock, causing large oscillations in both catches and CPUE. Lags between data and management actions and “latent years” are features of rules that reduce responsiveness. This study explores ways to improve the responsiveness of harvest control rules by using additional data to predict changes in vulnerable biomass. Four data sets are examined: CPUE trends, pre‐recruit indices, puerulus settlement indices, and size frequencies. Only pre‐recruit indices, which were explored with a simple delay‐difference model based on parameter estimates from recent assessments, appeared to have immediate potential for use in improving management procedures.

Validated estimation of growth and age in the New Zealand abalone Haliotis iris using stable oxygen isotopes

The growth and reproductive patterns of abalone are central to an understanding of the dynamics of their populations, and provide essential input into many of the stock assessment models currently used as the basis of assessing the sustainability of the fisheries. At present, most of this knowledge is obtained by tag-recapture methods, which are time consuming, often expensive and potentially confounding. The aim of the present study was to determine whether variations in the ratios of oxygen and carbon isotopes in the shells of Haliotis iris can be used to determine age, growth and reproductive patterns. Isotopic analyses of H. iris shells indicated that oxygen isotope profiles within the shells reflected ambient water temperature at the time of shell precipitation, and that these profiles could be used to determine age and growth patterns. To match the variation in isotopic ratios with ambient temperature cycles, we also adopted the novel approach of fitting a growth function to the data sets. The method should allow the collection of abalone growth information over the finer scales more appropriate for the rational management of abalone fisheries. Variations in the ratios of carbon isotopes showed no consistent patterns and, unlike some mollusc species, did not appear to be useful predictors of reproductive status at length.

Modelling the Flowering of Four Eucalypt Species Using New Mixture Transition Distribution Models

The multivariate relationship between the probability of flowering, in relation to two discrete states of rainfall and of temperature (high/low), is investigated via a mixture transition distribution (MTD) analysis, which allows for a different transition matrix for each lag (up to 12 months backwards in time) to present flowering via a so-called MTDg analysis. The conventional mixture transition distribution (MTD) model considers the effect of each lag to the present independently, and uses equal transition matrices among different lags. Flowering data consisted of monthly flowering records of E. leucoxylon, E. microcarpa, E. polyanthemos and E. tricarpa (1940 and 1970). We extend the MTDg model to allow for interactions (between rain and temperature) to account for changes in the transition matrices amongst the differing lags. The MTDg model with interactions shows that the flowering of E. leucoxylon and E. tricarpa behave similarly with temperature (both flower at low temperature) and have a positive relationship with flowering intensity 11 months ago. Eucalyptus microcarpa behaves differently, in that it flowers at high temperature. MTDg analysis also found a highly significant interaction between mean temperature and rainfall for E. polyanthemos, in that E. polyanthemos does not tend to flower during the winter time (when it is cold and wet). Rainfall has a direct positive impact only on E. tricarpa. These four species are influenced by temperature (and to a lesser extent rainfall) and as a consequence their flowering phenology will possibly change in response to climate change.