John Janssen

Recruitment Failure of Mottled Sculpin Cottus bairdi in Calumet Harbor, Southern Lake Michigan, Induced by the Newly Introduced Round Goby Neogobius melanostomus

This study documents a local extinction of mottled sculpins, apparently due to round gobies, and presents data pertinent to the mechanism of extinction. Mottled sculpins, Cottus bairdi, were assessed using SCUBA standardized diving transects during the invasion of the round goby, Neogobius melanostomus, into Calumet Harbor, southern Lake Michigan. Laboratory stream studies were conducted in which gravid male and female mottled sculpins were allowed to nest, then were exposed to one male round goby. Diet studies were conducted to assess the potential for competition for food at small sizes of both species. The SCUBA surveys showed that mottled sculpin populations rapidly declined, after the first round gobies were found in the area in 1994, despite the presence of a well established population prior to the round goby arrival. Mottled sculpins have been almost totally extirpated from the area in 1998 due to three proposed mechanisms: competition for food resources at small sizes, for space at intermediate sizes, and for spawning space at large sizes. The laboratory stream study confirmed that round gobies interfered with nest-guarding male mottled sculpins, seized their spawning shelters, changed to spawning coloration in preparation for spawning, and caused near loss of all the mottled sculpin eggs. It is concluded that recruitment failure and subsequent demise of mottled sculpins was most likely caused by spawning interference by round gobies.

Non-visual feeding behavior of the mottled sculpin, Cottus bairdi, in Lake Michigan

SynopsisField and laboratory experiments indicate that the mottled sculpin, Cottus bairdi, feed in the dark. Blinded sculpins feed on a variety of motile prey in the laboratory and show stereotyped responses to prey stimuli. The sculpins bite at moving inert objects, even if buried in substratum, indicating that they use their lateral line system to detect prey. Covering portions of the lateral line with an inert paste eliminates response to objects near the covered region of the lateral line. The sculpins can also detect prey (including inert objects) in a stream if the prey is upstream. Collection from two series of presunset, postsunset, presunrise, postsunrise, dives in Lake Michigan indicate nocturnal feeding by the mottled sculpin.

Behavioral and neurophysiological assessment of lateral line sensitivity in the mottled sculpin, Cottus bairdi.

Summary1.The unconditioned feeding response of the mottled sculpin, Cottus bairdi, was used to measure threshold sensitivity of the lateral line system to a vibrating sphere as a function of stimulus position (i.e. sphere near head, trunk or tail) and vibration frequency. In addition, extracellular recording techniques were used to measure threshold sensitivity curves for posterior lateral line nerve fibers for the same stimulus position used for measuring trunk sensitivity in behavioral measurements.2.For all stimulus positions, behaviorally-measured threshold sensitivity was relatively independent of vibration frequency from 10 to 100 Hz when defined in terms of water acceleration, rather than velocity or displacement. Best thresholds for stimuli placed 15 mm away from the head were around -75 dB re: 1 m/s2, approximately 20 dB less than that for stimuli placed at the same distance near the tail. Trunk sensitivity was intermediate.3.Physiologically-measured threshold sensitivity, in terms of acceleration, was also relatively independent of frequency from 10 to 100 Hz in most fibers. A smaller number of fibers showed a decline in acceleration sensitivity after 10–30 Hz, with the rate of decline being equivalent to equal velocity sensitivity. Best sensitivity of all fibers fell between -40 and -70 dB re: 1m/s2.4.These results indicate that (a) behavioral thresholds are based on acceleration-sensitive endorgans — most likely lateral line canal (rather than superficial) neuromasts, (b) behavioral performance can be accounted for on the basis of information from a single population of fibers, and (c) sensitivity varies along the fishs body in a manner that corresponds to the size and distribution of neuromasts.

Biophysical Model of Larval Yellow Perch Advection and Settlement in Lake Michigan

ABSTRACT Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage.

Form and Function Relationships in Lateral Line Systems: Comparative Data from Six Species of Antarctic Notothenioid Fish

The structure and physiology of the anterior lateral line canal systems were studied in six species of fish belonging to two different families within the suborder of antarctic fish Notothenioidei. Many of the canals within the species belonging to the genus Trematomus are relatively straight sided tubes with diameters around 0.4 mm. Some of the canals in Trematomus, and most of the canals in the icefishes (family Channichthyidae) are more complex. Relatively small pores lead into large tubules, the walls of which appear partially membranous, and the canals not much more than constrictions between adjacent tubules. Dissostichus mawsoni, a large species, has canals with distinctive wide and narrow sections, 1.8 mm and 0.48 mm, respectively. Despite these morphological differences the frequency response characteristics of anterior lateral line units are remarkably similar in all six species. In the case of D. mawsoni, this functional similarity results from narrow sections of the canals, which provide the viscous resistance to flow that preserves the mechanical filtering properties of the canal despite the huge size difference between D. mawsoni and the other species. It is argued that the most appropriate way to view canals is as high pass filters which attenuate lower frequencies, and that this effect is best illustrated by comparing the frequency response characteristics of superficial and canal neuromasts using a sinusoidal stimulus that has a constant peak-to-peak velocity. The functional contribution of canals is to attenuate low frequencies and improve the signal-to-noise ratio for biologically important signals in the presence of low frequency noise produced, for example, by the animals own movements.

Anatomy and differential growth of the lateral line system of the mottled sculpin, Cottus bairdi (Scorpaeniformes:Cottidae)

Scanning electron microscopy and standard histological techniques were used to describe the basic anatomy and postembryonic growth of the lateral line system of Cottus bairdi. The gross anatomy and distribution of lateral line neuromasts in canals and superficially on the skin are similar to what has been reported for many primitive actinopterygian fishes. Both canal and superficial neuromasts showed postembryonic growth in the number of hair cells and size of neuromasts, but canal neuromasts grew more elongate whereas superficial neuromast grew symmetrically. Neuromasts in the mandibular canal grew significantly faster than any other neuromasts and superficial neuromasts on the head showed the least amount of growth. Differential growth of the sculpin lateral line system may be related to the feeding behavior of the animal and to differences in the ambient levels of water noise to which larval and adult fish are exposed.

Impact of Round Gobies (Neogobius melanostomus) on Dreissenids (Dreissena polymorpha and Dreissena bugensis) and the Associated Macroinvertebrate Community Across an Invasion Front

ABSTRACT We studied the impact of round gobies (Neogobius melanostomus) on lithophilic invertebrates (having an association with a stony substrate) across an invasion front along the Door Peninsula, which flanks eastern Green Bay, Lake Michigan. We conducted both a cross-invasion front field survey and a rock-transfer experiment. For the field survey, we collected pairs of rocks from ten sites, including sites north of the invasion front and south of the invasion front. Zebra mussels (Dreissena polymorpha), quagga mussels (D. bugensis), and non-mussel invertebrates were removed from the rocks and enumerated. The rocks were measured and the algae removed and weighed. Round gobies were censused by videotaping along transects. There was a statistically significant negative relationship with round goby abundance for most invertebrates, including zebra mussels, quagga mussels, isopods, and snails, with the result for amphipods being suggestive. For the experiment, we transferred 20 rocks in bags from a round goby “absent” site with 10 going to a round goby abundant site and 10 being returned to the original site. The rocks incubated overnight, invertebrates were removed the next day, and the rocks were measured. There were significantly fewer zebra mussels, quagga mussels, isopods, amphipods, and snails from the rocks incubated at the round goby abundant site compared to those returned to the round goby-free site. Thus, the results of the survey and rock-transfer experiment suggest that round gobies are influencing the benthic macroinvertebrate abundance through predation. The negative impact on mussels is probably due to direct predation while the negative impact on the other invertebrates may be a combination of direct predation and indirect effects due to the loss of the microhabitat or food that zebra mussels produce.

Lake Sturgeon Age Validation using Bomb Radiocarbon and Known-Age Fish

Abstract Pectoral fin spines have been the accepted structure for estimating the age of various sturgeon species for nearly 100 years, though other structures have also been used (otoliths, pectoral girdle, scutes, and caudal fulcra). Accuracy of age estimates using any of these structures has not been validated, so we report the first use of bomb radiocarbon (14C) assays to assess the validity of ages estimated using growth increments on pectoral fin spine and otolith frontal cross sections from lake sturgeon Acipenser fulvescens; we also assessed age estimates from pectoral fin spines of known-age lake sturgeon. Growth increments on pectoral fin spine cross sections underestimated true age of fish older than 14 years and error increased with age, whereas otoliths accurately estimated true age up to at least 52 years. Increment formation on pectoral fin spine and otolith cross sections from juvenile lake sturgeon (ages 2-11) was similar, although pectoral spines were clearer and easier to interpret. A po...

Functional and Evolutionary Implications of Peripheral Diversity in Lateral Line Systems

Any treatise on the evolution of hearing inevitably raises the possibility that the vertebrate auditory system has evolved from the mechanosensory lateral line system known to exist in the earliest vertebrates. The arguments for (van Bergeijk 1967; Jorgensen 1989) and against (Wever 1976; Northcutt 1981) this “octavolateralis” hypothesis, first proposed by Ayers (1892), have depended primarily on anatomical and developmental comparisons between the two systems. It is questionable whether this issue can or ever will be resolved, but the frequency with which it has been addressed in the past and is currently being addressed in this volume (Popper, Piatt, and Edds, Chapter 4; Fritzsch, Chapter 18) testifies to the fascination it holds for anyone interested in the evolution of ears and hearing.

Lateral line receptivity in the mottled sculpin (Cottus bairdi)

We studied the lateral line receptive field of the mottled sculpin (Cottus bairdi) to live Daphnia magna and to an inert vertically vibrating bead. Both stimuli elicited feeding responses when near the head or trunk but response to stimuli near the trunk extended only as far as the posterior limit of the lateral line (beneath the soft dorsal fin). The sculpin was significantly less responsive to stimuli for the region in front of the snout compared to the side of the head. The region in which the sculpin strikes (strike zone) at prey extended slightly posterior to the mouth and occupied a mean area of 16.0 mm2 for Daphnia, 14.1 mm2 for the bead (both based on four fish). Prey detected outside this region elicited repositioning by the fish so that the preys original location was in the strike zone.