Available online at www.nznaturalsciences.org.nz Influence of open and closed river systems on the migrations of two northern New Zealand populations of banded kokopu (Galaxias fasciatus) Raymond Tana1 and Brendan J. Hicks2 Centre for Biodiversity and Ecology Research, Department of Biological Sciences, Faculty of Science and Engineering, The University of Waikato, Hamilton 3240, New Zealand. Email addresses: [email protected], [email protected] (Received 31 January 2012, revised and accepted 10 April 2012) Abstract Otolith microchemical analysis by laser ablation inductively coupled mass spectrometry (ICP-MS) was used to investigate the migratory life histories of banded kokopu (Galaxias fasciatus) in two streams on the North Island of New Zealand. Known differences in marine and freshwater chemistry were used as a premise to document the migratory life strategies of banded kokopu between these environments. More specifically, temporal trends in high and low strontium/calcium ratios (Sr/Ca) identified in fish otoliths were used to determine evidence of migration between fresh and saltwater environments. Trace element analysis of fish captured above the Whau Valley Reservoir reflected non-migratory life histories and exhibited consistently low Sr/Ca ratios across the entire otolith. However, one fish from above the reservoir indicated unusually high Sr/Ca ratios in early adulthood. These high Sr levels were attributed to localised inputs from mineral-rich seepages associated with past mining practices in the region and low calcium availability within the Pukenui Stream. Otoliths from banded kokopu collected from Komiti Stream were shown to be migratory with a marine larval stage (high Sr/Ca ratio levels at the otolith nucleus), followed by a freshwater adult phase (low Sr/Ca ratio levels towards the edge) indicating their amphidromous origins. The study provides further evidence of non-diadromous recruitment for banded kokopu as a consequence of a large in-stream barrier and will add to the known distribution of landlocked species in New Zealand. Key words: Banded kokopu – Galaxias fasciatus – diadromy – otolith microchemistry – landlocked – laser ablation ICP-MS Introduction followed by ten of New Zealand’s eighteen diadromous fish species (McDowall 1993; The amphidromous lifecycle of 1995). Typically, strategies involving fish banded kokopu (Galaxias fasciatus) is movement between fresh and saltwater representative of life history patterns environments are termed ‘diadromy’ New Zealand Natural Sciences (2012) 37: 25-36. © New Zealand Natural Sciences 26 New Zealand Natural Sciences 37 (2012) (McDowall 1988; 1990; 1996). More ple forms of larval recruitment in giant specifically, an amphidromous life kokopu (Galaxias argenteus) collected strategy is characterised by spawning from the lower Taieri and Mataura River and egg development in freshwater catchments in Southland Otago. Aside followed by a marine growth phase (as from identifying typical diadromous hatchlings) returning several months movements in fish, their study indicated later as upstream migrant juveniles to that non-diadromous recruitment may mature in freshwater (McDowall 1995; also play an important role in sustaining 2007). For researchers, the task of coastal populations of giant kokopu in documenting movement patterns of this the region (David et al. 2004). Similarly, type can be difficult, particularly where otolith chemical analysis of common fish may range over large temporal and bully (Gobiomorphus cotidianus) by Closs spatial scales. Furthermore, such life et al. (2003) collected from the same strategies preclude conventional tagging general sample locations as David et al. methods due to size limitations in tagging (2004), provided further evidence of technology, costs and the inability to diadromous and non-diadromous recruit- effectively track larval fish throughout ment. This was later shown to be the case time and space (Thorrold. et al. 1998; for common bully in Lake Tarawera and Munro 2004). the Tarawera River on the North Island However, microchemical analysis of of New Zealand (Michel et al. 2008). In fish otoliths offers another approach as the present study, we set out to expand otoliths act as natural tags recording in the current information on the migratory chronological sequence daily growth life strategies of banded kokopu caught increments composed of trace elements within an open and closed river system present in the water throughout a fish’s using otolith microchemistry techniques. life (Campana 1999; Campana & Thor- More specifically, we compare 88Sr:43Ca rold 2001). Furthermore, once chemical ratios in otoliths of fish taken above a elements are deposited in the otolith they large 65 m high dam near Whangarei are neither resorbed nor re-metabolized, City (with no upstream access from the resulting in a permanent chemical record sea) with fish from a small stream in the of the fish’s life history (Campana 1999; Kaipara Harbour (with sea access) on the Campana & Thorrold 2001). For this North Island of New Zealand. reason, the ratio of Sr over Ca (Sr/Ca), can be used to describe fish movements Methods between fresh and saltwater environ- ments particularly as Sr concentrations Fishing sites are higher in seawater (0.088 ppm), than freshwater (0.00018 ppm), (Tzeng 1996; Banded kokopu were collected from the Tzeng et al. 2005). Pukenui Stream located above the Whau In New Zealand, a growing number Valley Reservoir near Whangarei on the of studies have used Sr/Ca ratios to elu- east coast and from Komiti Stream in cidate diadromous life histories for several the Kaipara Harbour on the west coast freshwater fish species. Davidet al. (2004) of northern New Zealand (Figure 1). used Sr/Ca ratios to identify the princi- The Whau Valley Reservoir (25 ha) Tana & Hicks: Open and closed populations of banded kokopu 27 was constructed in the early 1950s in labelled containers in 70% ethanol for by the Whangarei District Council as transport to the lab. the main water supply for Whangarei Otolith extraction and polishing residents. Three headwater streams feed into the Pukenui Stream before entering Sagittal otolith pairs were extracted the reservoir from the Pukenui Forest from fifteen banded kokopu (Table 1). Reserve (NZMS260 Topographic Map, The head of each fish was sectioned 1:50,000 Q07, Q08). From the reservoir with a scalpel along the midline dorsal outlet the Pukenui Stream descends 65 surface (from the head to the mouth), m into the Waiarohia Stream and the and separated to expose left and right Whangarei Harbour. Fish species above cranial cavities. Brain tissue was carefully the reservoir include banded kokopu flushed out with distilled water using a (Galaxias fasciatus), rainbow trout pipette, exposing the brain cavity and (Onchorynchus mykiss) and the longfin inner ear. Left and right otolith pairs eel (Anguilla dieffenbachii), (Manning were then removed from both cavities 1996). However, in the Waiarohia using fine-tip tweezers under a compound Stream immediately below the reservoir microscope. Excess tissue was removed banded kokopu are not present. Instead and otoliths were rinsed thoroughly in a population from Komiti Stream in the distilled water before being stored in Kaipara Harbour was sampled (Figure 1). labelled vials to air-dry for 24 h. Otoliths The surrounding catchment of Komiti were then embedded in thermosetting Stream is primarily pine forest (Pinus glue (Crystalbond, Aremco Products, radiata) with a small residential area Inc, USA) and mounted on glass slides leading to the river mouth. We selected (3 per slide), labelled by date and stream this stream because it had no in-stream site using a glass etching drill and left barriers (waterfalls or culverts and dams) overnight to dry. Otolith polishing was that would prevent fish passage from the carried out systematically using firstly sea. Eight fish from Pukenui Stream above 1200, 2000, and then 4000 grain wetted the reservoir and seven from Komiti carborundum sand paper to expose the Stream were collected on 1 July and 10 otolith nucleus (area representing the October 2006 (Table 1), using minnow larval growth phase in fish) for chemical traps (4 mm mesh), baited with Kraft analysis. Vegemite®, and by spotlighting. For each Laser ablation ICP-MS day of sampling, traps were set before sunset along the Pukenui Stream and in Chemical analysis of fish otoliths was the Komiti Stream. Within the first hour conducted at the University of Waikato’s after sunset, spotlighting was carried out Mass Spectroscopy Suite using a Perkin along shallow (< 600 mm depth) stream Elmer Elan SCIEX DRCII inductively reaches and banded kokopu identified coupled mass spectrometer (ICP-MS) by spotlight were carefully scooped up with a New Wave Research Nd: YAG by dip net (5 mm mesh). Fish captured 213 nm wave length laser. Only six (by both methods) were anaesthetised in otoliths from Komiti Stream and six benzocaine until dead, measured to the from Pukenui Stream were suitable for nearest mm total length (TL), and placed analysis after sustaining damage during 28 New Zealand Natural Sciences 37 (2012) Figure 1. Location of banded kokopu fishing sites in the Pukenui Stream above Whau Valley Reservoir near Whangarei on the east coast and Komiti Stream in the Kaipara Harbour on the west coast of northern New Zealand. the polishing and ablation process. To standards, a single line of spots across minimise the need to repeatedly open the otolith growth axis starting from the the