Fish Usage of Estuarine and Coastal Habitats

320+ sites spread across 31 estuaries (with another 40-50 planned in the future) in the northern North Island are sampled for small fish assemblages. This data is being used to construct a fish-habitat classification. More than 40 species are sampled including juvenile snapper gurnard, trevally, kahawai, mullets, flounders and soles. Substantial abundance and diversity changes occur along gradients from clear water-sandy habitats to more turbid water-muddy habitats. This has important implications for sedimentation effects on fish habitats. Purpose: To determine large-scale spatial patterns of small fish abundance in estuarine systems. To determine what factors influence fish distribution and abundance. To build a fish-habitat classification. To make predictions about which species occur where and why.

Sampling sites were selected along expected environmental gradients within harbours and sampled with seine nets. Variable measured are: Distance towed, Water depth, Slope, Substrate type, Presence of seagrass and mangroves, Dissolved oxygen, Water temperature, Salinity, Turbidity (Secchi), Estuary type, Water area, volume and mean depth, Spring tidal prism, Ratio tidal prism to estuary volume, Circumference and shoreline complexity, Tidal versus river forcing ratio, Tide range, Intertidal habitat (% mud, sand, mangroves, swamp), Catchment area, vegetation, rainfall, temperature, wind and geology, Estuary wave climate and fetch. Waikato estuaries included in the study are Firth of Thames, Coromandel, Whangapoua, Whitianga, Whangamata, Tairua and recently Port Waikato, Raglan, Kawhia and Aotea.

northern North Island estuaries

Waikato Region: Upper Firth – 2728125, 6440838, NZMG, 1:100,000, AREA Coromandel – 2731161, 6487197, NZMG, 1:50,000, AREA Manaia – 2729391, 6480968, NZMG, 1:50,000, AREA Kennedy Bay – 2739796, 6499375, NZMG, 1:50,000, AREA Whangapoua – 2745181, 6493816, NZMG, 1:50,000, AREA Whitianga – 2750534, 6477849, NZMG, 1:50,000, AREA Whangamata – 2764538, 6442493, NZMG, 1:50,000, AREA Tairua – 2764599, 6462659, NZMG, 1:50,000, AREA

25 estuaries were sampled in 2001, 6 more in 2003, with another 40-50 planned.

Fine mesh (9mm) beach seines were pulled by hand along the low tide beach during late summer. Sampling was undertaken 2.5 hours either side of low tide. Sampling sites selected along expected environmental gradients within harbours. Frequency of collection: Annually during March-April

Not reported Gaps in collection: Not reported Data quality: Analyses restricted to fish <250mm long, plus larger sand flounder and yellow-belly flounder (99.5% of fish caught), to avoid problems with net avoidance. Attribute accuracy: Not reported Completeness: Not reported

electronic, maps Digital Format: Oracle, GIS (ArcView) - positional data

Will be used to predict land use effects on fish communities and habitats.

Contact NIWA Sensitivity/Confidentiality: Contact NIWA

Ongoing, further surveys planned for 2004.

Additional comments: Various gobies caught during survey, some of which are probably introduced through ballast water. Acentrogobius pflaumii Sujihaze goby has been caught in Whangapoua Harbour. Another 40-50 estuaries are planned to be suveyed in the future. Emerging evidence of importance of low intertidal/subtidal seagrass to juvenile snapper.