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Many fish species rely on estuarine nursery habitats as they transition to adult life stages. Quantifying nursery value, however, requires identification of the life stages (often small and short-lived) that utilise nursery habitats, and survey methods that provide comparable estimates across habitats. We focused our surveys on post-settlement snapper (Chrysophrys auratus) using video camera deployments across habitats within a northeastern New Zealand harbour. Post-settlement snapper abundance was higher among structured habitat types relative to bare sediments, with the type of structured habitat not influential. The exception appeared to be for reef habitat (although sampling was limited). Reef sites were structurally complex, but largely inhabited by older life stages (snapper and other fish species). Overall, nursery value for snapper appears to be connected to structure, rather than structure type. This result emphasises the importance of a broadened scope to coastal fishery management, one ...

Juvenile fish nurseries are an essential life stage requirement for the maintenance of many fish populations. With many inshore habitats globally in decline, optimising habitat management by increasing our understanding of the relationship between juvenile fish and nursery habitats may be a prudent approach. Previous research on post-settlement snapper (Chrysophrys auratus) has suggested that structure may provide a water flow refuge, allowing snapper to access high water flow sites that will also have a high flux of their pelagic prey. We investigated this hypothesis by describing how Artificial Seagrass Units (ASUs) modified water flow while also using a multi-camera set up to quantify snapper position in relation to this water flow environment. Horizontal water flow was reduced on the down-current side of ASUs, but only at the height of the seagrass canopy. While the highest abundance of snapper did occur down-current of the ASUs, many snapper also occupied other locations or were too high in the water column to receive any refuge from water flow. The proportion of snapper within the water column was potentially driven by strategy to access zooplankton prey, being higher on the up-current side of ASUs and on flood tides. It is possible that post-settlement snapper alternate position to provide opportunities for both feeding and flow refuging. An alternative explanation relates to an observed interaction between post-settlement snapper and a predator, which demonstrated that snapper can utilise habitat structure when threatened. The nature of this relationship, and its overall importance in determining the value of nursery habitats to post-settlement snapper remains an elusive next step.

Management of fish populations is often focused on the exploitation of adult fish. Maintaining the habitat requirements of all life stages may also be an important consideration. We investigated the value of structured habitat to juvenile fishes within a northeastern New Zealand harbour using artificial seagrass units (ASUs). Specifically, we deployed ASUs across treatments with high vs. low habitat manipulations. We hypothesised that if the abundance of recruiting juvenile fishes was greater on the high habitat availability treatments this would suggest that the availability of habitat was limiting juvenile fish abundance. Our analyses were focused on the four most abundant fishes that settled on our ASUs: snapper (Pagrus auratus); spotty (Notolabrus celidotus); trevally (Pseudocaranx dentex); and an assemblage of pipefish species. For snapper, spotty and pipefish, abundance was greater on the high habitat availability treatments. This result would be unlikely to occur if the availability of juvenile fis...

Estuarine and sheltered coastal habitats that contain physical structure are potentially important nurseries for juvenile fish. Many of these structured habitats, however, are potentially vulnerable to stressors such as elevated turbidity. Quantifying the benefits that structured habitats provide to juvenile fish may therefore be an important step in the management process. We investigated the value of structured habitat for juvenile fishes in northeastern New Zealand, using artificial seagrass units (ASUs) with varying blade density. ASUs were predominantly settled by juvenile snapper (Pagrus auratus) and spotty (Notolabrus celidotus). The density of both snapper and spotty was greatest on ASUs with the highest blade density. For snapper, a gradient in abundance was present (with higher abundance closer to the harbour mouth), suggesting either a gradient in the supply of recruits or a potential recruitment shadow effect. The size distribution of juvenile snapper (12–70 mm fork length) was very similar on both sampling trips, despite the 2-month interim period, suggesting an ontogenetic habitat shift dependent on size. The condition of juvenile snapper from ASUs with the highest blade density was also greater than the other ASU treatments. Overall, these results provide new empirical evidence that habitats with physical structure within shallow estuarine systems are important to early stage juvenile fishes such as snapper, and indicate that the location-specific context of that habitat is also likely important.

Nursery habitats provide elevated survival and growth to the organisms that associate with them, and as such are a crucial early life-stage component for many fishes and invertebrates. The exact mechanisms by which these benefits are afforded to associated organisms, however, are often unclear. Here we assessed potential explanations of the nursery function of structurally complex habitats for post-settlement snapper, Chrysophrys auratus, in New Zealand. Specifically, we deployed Artificial Seagrass Units (ASUs) and used a combination of video observation, netting and diet analysis of associated post-settlement snapper as well describing potential prey within the micro-habitats surrounding ASUs. We did not observe any predation attempts and few potential predators, suggesting that for snapper the nursery value of structurally complex habitats is not as a predation refuge. The diet of post-settlement snapper mostly consisted of calanoid and cyclopoid copepods, which were most commonly sampled from within the water column. Nearly all suspected feeding events were also observed within the water column. When considering the velocity of water flow at each ASU, plankton sampling revealed a greater availability of copepods with increasing current strength, while netting and video observation demonstrated that the abundance of snapper was highest at sites with intermediate water velocity. This study highlights that the interaction between water flow and food availability may represent an important trade-off between energy expenditure and food intake for post-settlement snapper. Structurally complex habitats may mediate this relationship, allowing snapper to access sites with higher food availability while reducing swimming costs. This mechanism may have broader relevance, potentially explaining the importance of estuarine nursery habitats for other species.

The Asian goby, Acentrogobius pflaumii (Bleeker, 1853), is reported from New Zealand waters for the first time. It was collected by beach seine in 2001–02 from muddy substrata in the upper reaches of the Waitemata and Whangapoua Harbours. We suggest that A. pflaumii has been introduced to New Zealand, probably in ship ballast water. It may have arrived directly from its native range in the north‐west Pacific Ocean, or indirectly via Australia, which it invaded before 1996. The Australian bridled goby, Arenigobius bifrenatus (Kner, 1865), which is also thought to have invaded New Zealand via ballast water, is here recorded from three new locations, extending its known New Zealand range to five different harbours spanning c. 150 km of coastline. This species is more widespread than previously thought and appears well established. Both gobies have been found only on the east coast of the North Island.