Thermal and asphyxia exposure risk to freshwater fish in feral‐pig‐damaged tropical wetlands

Abstract

Acute thermal and asphyxia exposure risks for freshwater fish occupying three tropical wetland typologies were examined. Field water-quality data revealed that fish in wetlands grazed by pigs had the highest exposure risks, because they are shallow and heavily damaged by pig activities. In contrast, with the exception is dissolved oxygen (which still reached critical conditions because of aquatic vegetation respiration), deeper permanent and pig-managed wetlands provides the best opportunity for the same fish species to survive in a heavily pig-modified tropical landscape.

Feral pig exclusion fencing provides limited fish conservation value on tropical floodplains

“…The duration, timing and frequency that off channel wetlands maintain lateral pulse connection to primary rivers is an important determining factor in broader contribution to coastal fisheries production [6–9]. In addition to connection, environmental conditions become important including water quality [10], access to shelter to escape predation and available food resources [11, 12]. Efforts by managers to restore wetland ecosystem values is increasing, nevertheless access to data establishing success of these programs are limited, which becomes important when attempting to establish biodiversity returns for the funding investment made by government or private investor organisations [13–15].…”

“…In tropical north Australia, seasonal off channel wetlands are more pronounced owing to high evaporation rates, loss to groundwater [19], and in many situations waters quickly retract away from the banks and riparian shade [16]. At that point, it is thought that they become more prone to reduced water quality conditions - most notably reduced water depth [18], and high water temperatures [10, 20]. This increases aquatic fauna exposure risks to acute and chronic thresholds [21, 22].…”

“…This increases aquatic fauna exposure risks to acute and chronic thresholds [21, 22]. In the late-dry season, fish confined to isolated wetlands on floodplains therefore have very limited avoidance options [10], unlike other fauna such as the freshwater crab also occupying seasonal tropical rivers in northern Australia, that will employ terrestrial re-location and access burrows when confronted with thermoregulation [23]. Fish must exploit available ephemeral aquatic habitats [24, 25], which can be specific to each wetland depending on orientation and location [26], depth and vegetation cover in the landscape [20], in order to survive until monsoonal rain reconnects overbank river networks again.…”

“…This feeding strategy has a massive impact on wetland aquatic vegetation [30], which gives rise to soil erosion and benthic sediment re-suspension, reduced water clarity and eutrophication which becomes particularly critical late-dry season. The fact that limited data exits on the impact that feral pigs contribute to wetlands [31–34], places a strain on the ability for land managers to quantify the consequences of pig destruction [35]. Conversely, a lack of baseline data means quantifying success following expensive mitigation efforts is difficult.…”

“…The aims were twofold: first to determine whether the model of non-randomness of fish stands here in wetlands, and secondly whether specific environmental conditions influence fish composition in wetlands with and without fences. These data are important and necessary given increasing government funding investment underway and planned in northern Australia for restoration of wetlands impacted by feral animals (including pigs) [10].…”