Bruce Hartill

Diurnal and tidal movements of snapper (Pagrus auratus, Sparidae) in an estuarine environment

Using individually coded acoustic transponders and an array of 15 moored receivers (detection range ∼300 m), the temporal and spatial movements of the temperate snapper Pagrus auratus (Sparidae) were studied within an estuary. Of the 28 fish initially tagged, 20 were subsequently detected within the study area for up to 70 days. The spatial scale of daily movements was in the order of hundreds of metres for most fish, suggesting relatively restricted home ranges over the period monitored (November-January). The detectability of fish remaining in the estuary was lower at night, probably because of fish moving out of the main channel and onto surrounding shallow banks during darkness. Temporal movement patterns detected using spectral analyses (Fast Fourier Transforms) were predominantly diurnal, with subordinate tidal behaviour also evident in some fish. These results demonstrate that in this system, snapper occupy relatively small (hundreds of metres) and discrete areas of soft sediment seafloor, within which repeated, predictable movements are made. Variability among fish has highlighted the need for a better understanding of the relationship between fish behaviour and fine-scale habitat features (metres).

MODIFICATION OF MARINE BENTHOS BY TRAWLING: TOWARD A GENERALIZATION FOR THE DEEP OCEAN?

Anthropogenic disturbance of deep-sea benthic systems, especially by fish- ing, has increased markedly in the last 40 years. Deep-sea mining and extraction of fossil fuels can occur at extraordinary intensity at individual sites, but the large number of fishing vessels and their mobility probably makes commercial trawling the most pervasive of our marine activities to depths of up to about 1200 m. Knowledge of the effects of trawling on soft-sediment, benthic communities is, however, limited to shallow, coastal systems, mostly at small spatial scales. We extend that knowledge to deeper systems at the scale of commercial fishing by assessing the effects of bottom trawling in northeastern New Zealand. We characterized the invertebrate catch of 66 research trawls spread along 220 km of continental slope in depths of 200-600 m (encompassing about 2400 km 2 ). At each site, we indexed the intensity of previous trawling using trawl-by-trawl fishing returns. A suite of multivariate analyses revealed that fishing activity was negatively associated (after ex- cluding the effects of depth and location) with invertebrate species richness and diversity and with the density of several taxa. Our models explained up to two thirds of the variation in the invertebrate catch of research trawls. After excluding the effects of depth and location, we attributed 11-40% of total variation to fishing. Concordance among the results of several multivariate methods based on different analytical approaches and assumptions reveals a strong and coherent pattern in the data that is consistent with the predicted and observed effects of trawl fisheries and other sources of physical disturbance. We infer that trawling probably changes benthic community structure and reduces biodiversity over broad spatial scales on the continental slope as well as in coastal systems. Such effects would have important implications for local and regional biodiversity and for the development and management of sustainable fisheries.

Snapper (Chrysophrys auratus): a review of life history and key vulnerabilities in New Zealand

Snapper (Chrysophrys auratus) is an important coastal fish species in New Zealand for a variety of reasons, but the large amount of research conducted on snapper has not been reviewed. Here, we review life history information and potential threats for snapper in New Zealand. We present information on snapper life history, defining stages (eggs and larvae, juvenile and adult), and assess potential threats and knowledge gaps. Overall we identify six key points: 1. post-settlement snapper are highly associated with certain estuarine habitats that are under threat from land-based stressors. This may serve as a bottleneck for snapper populations; 2. the largest knowledge gaps relate to the eggs and larvae. Additional knowledge may help to anticipate the effects of climate change, which will likely have the greatest influence on these early life stages; 3. ocean acidification, from land-based sources and from climate change, may be an important threat to larval snapper; 4. a greater understanding of population connectivity would improve certainty around the sustainability of fishery exploitation; 5. the collateral effects of fishing are likely to be relevant to fishery productivity, ecosystem integrity and enduser value; 6. our understanding of the interrelationships between snapper and other ecosystem components is still deficient.

Scale- and context-dependent selection of recreational harvest estimation methods: the Australasian experience.

Abstract Fisheries managers are becoming increasingly aware of the need to quantify all forms of harvest, including that by recreational fishers. This need has been driven by both a growing recognition of the potential impact that noncommercial fishers can have on exploited resources and the requirement to allocate catch limits between different sectors of the wider fishing community in many jurisdictions. Marine recreational fishers are rarely required to report any of their activity, and some form of survey technique is usually required to estimate levels of recreational catch and effort. In this review, we describe and discuss studies that have attempted to estimate the nature and extent of recreational harvests of marine fishes in New Zealand and Australia over the past 20 years. We compare studies by method to show how circumstances dictate their application and to highlight recent developments that other researchers may find of use. Although there has been some convergence of approach, we suggest th...

Aquaculture trials of the New Zealand bath‐sponge Spongia (Heterofibria) manipulatus using lanterns

Abstract A submarine lantern system was trailed in the aquaculture of explants of the endemic New Zealand bath‐sponge Spongia (Heterofibria) manipulatus (Demospongiae: Dictyoceratida: Spongiidae) at four New Zealand sites, two in the Marlborough Sounds and two off Coromandel Peninsula. The main objectives were to compare growth rates of explants at different sites, compare these with those of control sponges, and to assess the utility of these lanterns for the culture of this species. After a period of 13 months, sponges at exposed Bonne Point in the Marlborough Sounds were on average 73% larger in estimated volume than at the start of the experiments. Growth rates of explants at exposed Port Charles, Coromandel, showed no significant change over the study period, although positive growth over spring 2003 was evident. Sponge explants at sheltered Wairangi Inlet and Kennedy Bay, in the Marlborough Sounds and Coromandel, respectively, did poorly, with most explants regressing in size and becoming moribund. Growth rates varied considerably between individuals at each location. Implications of the growth rate characteristics of S. (H.) manipulatus, and the design and construction of the aquaculture lantern, for the future commercial production of this species are discussed.

Refining and Applying a Maximum-Count Aerial-Access Survey Design to Estimate the Harvest Taken from New Zealand's Largest Recreational Fishery

Abstract We used a maximum-count aerial-access survey design to estimate the 12-month recreational harvest of snapper Chrysophrys (Pagrus) auratus (also known as squirefish) taken by New Zealands largest recreational fishery. To provide a count of all boats fishing on a given day, the spatial extent of the 3,800-km2 Hauraki Gulf embayment was surveyed from the air on a random stratified selection of survey days at the approximate time of maximum effort. Anglers were also censused at a subset of the available access points on the same day. The ratio of the aerial count to the number of interviewed parties who claimed to have fished at the time of the overflight was used to expand the observations of landed catch and to estimate the total catch taken by all fishers returning to all access points. Pairing an aerial count with a creel-survey-derived profile of effort on each survey day provides two advantages. First, only one flight is required to estimate the overall level of effort on each day, which is be...

Adaptive Background Modeling for Land and Water Composition Scenes

In the context of maritime boat ramps surveillance, this paper proposes an Adaptive Background Modeling method for Land and Water composition scenes (ABM-lw) to interpret the traffic of boats passing across boat ramps. We compute an adaptive learning rate to account for changes on land and water composition scenes, in which the portion of water changes over time due to tidal dynamics and other environmental influences. Experimental comparative tests and quantitative performance evaluations of real-world boat-flow monitoring traffic sequences demonstrate the benefits of the proposed algorithm.

Class-Wised Image Enhancement for Moving Object Detection at Maritime Boat Ramps

In the context of marine boat ramps traffic surveillance, we propose in this paper a novel image enhancement method for interpreting the traffic of boats passing across the boat ramps. As the background dynamics of land and water scenes differ markedly, this new approach classifies areas in each image as either land or water, so that different strategies can be adopted to enhance image on land and on the water, respectively. In particular, the use of the dynamic sharpening size and adaptive sharpening strength significantly increases the robustness of this enhancement method. Experimental results demonstrate that our method is much more able to cope with the highly dynamic land and water composition scenes compared with the state-of-the-art methods.

Object Trajectory Association Rules for Tracking Trailer Boat in Low-frame-rate Videos

Tracking object accurately in one frame per minute (1-fpm) video is believed to be impossible, because the one-minute discontinuity of object coupled with dynamic background variation implies that the motion and appearance of target is theoretically not predictable. In the context of maritime boat ramps traffic surveillance, we propose in this paper a novel approach to tracking object in the low-frame-rate (LFR) of 1-fpm videos, where the motion discontinuity of object is mitigated by adopting target lifespan path-template and association rules of behavior prediction. The approach has been applied to trailer boat counting at three maritime boat ramps in New Zealand. The obtained accuracy goes above 90 %, with reference to the ground truth manual counting.

A Combo Object Model for Maritime Boat Ramps Traffic Monitoring

Conventional tracking methods are incapable of tracking boats towed by vehicles on boat ramps because the relative geometry of these combined objects changes as they move up and down the ramp. In the context of maritime boat ramp surveillance, fishing trailer boat is the object of interest for monitoring the amount of recreational fishing activities over the time. Instead of tracking trailer boat as a single object, this paper proposes a novel boat-vehicle combo object model, by which each boat is tracked as a combination of a trailered boat and a towing vehicle, and the relationship between these two components is modelled in multi-feature space and traced across consecutive frames. Experimental results show that the proposed combo modelling tracks the object of interest accurately and reliably in real-world boat traffic videos.